427 tall deck in a 1979 K25 GMC - The 1947 - Present Chevrolet & GMC Truck Message Board Network

Puke160 · 11-30-2014, 05:19 PM

I'm in the process of rebuilding a 427 tall deck to put in my K25. I am trying to find out if I can*use the 13" clutch assembly and flywheel out of the C70. Also if there is a dual plane low rise intake for the tall decks, so I don't have to use the spacers. And will the radiator out of a 2 ton fit in my truck. Also header fitment. The truck will be used to pull a stock trailer and as a wood truck. So the setup should work good as long as everything fits.

mrolds88 · 11-30-2014, 08:41 PM

You can use the clutch, but you have to use the rest of the transmission stuff too. The 13" clutch uses a larger bellhousing, This requires the steel adapter ring and the MD bellhousing and the MD trans as the input shaft is bigger. It is a benefit for you though. Headers I cant help you with, ,nor the intake. One last thing, I seem to remember that the 5 speed overdrives from a military deuce and a half are supposed to bolt up to that bellhousing.

bdiamond · 12-01-2014, 03:00 PM

Unless you set the engine really high I bet you'll be hard pressed to find a pair of headers that fit inside the frame rails.

Puke160 · 12-01-2014, 04:06 PM

If I use the MD transmission then I can't use my 205 transfer case because of the output shaft. I don't know about the military 5 speed. The truck spends 90 percent of its life in dirt, mud, or snow. I need the 4 wheel drive. And hooker make a set of headers of a standard big block swap in this truck. I call them twice, jegs, and summit and everyone I talked to said they don't know if they would fit.

mrolds88 · 12-01-2014, 09:33 PM

I totally missed the "K" part. Doh!!! You are right about the 5 speed. HOWEVER there may be an out for you. GM put SM465's in the big trucks with the 13" clutch. With that said, you may be able to simply swap the input shaft and be done. Or you may be able to swap output housing and output shaft onto the big truck 4 speed. That would do it for you.

Puke160 · 12-02-2014, 01:07 AM

The truck has a sm465 in it but I think it's a 12" clutch not the 13" but if they useed the sm465 in the medium duty trucks it should be a pretty easy swap. It's coming out along with the np205 to be rebuilt and beefed up some.

78maliburat · 12-04-2014, 02:38 PM

I have a tall deck 427 in a 85 and jegs brand headers fit nice no issues

11-30-2014, 05:19 PM	#1
Puke160 Registered User Join Date: Nov 2014 Location: Paola, ks Posts: 42	427 tall deck in a 1979 K25 GMC I'm in the process of rebuilding a 427 tall deck to put in my K25. I am trying to find out if I can*use the 13" clutch assembly and flywheel out of the C70. Also if there is a dual plane low rise intake for the tall decks, so I don't have to use the spacers. And will the radiator out of a 2 ton fit in my truck. Also header fitment. The truck will be used to pull a stock trailer and as a wood truck. So the setup should work good as long as everything fits.

11-30-2014, 08:41 PM	#2
mrolds88 Registered User Join Date: Jul 2011 Location: WV Posts: 946	Re: 427 tall deck in a 1979 K25 GMC You can use the clutch, but you have to use the rest of the transmission stuff too. The 13" clutch uses a larger bellhousing, This requires the steel adapter ring and the MD bellhousing and the MD trans as the input shaft is bigger. It is a benefit for you though. Headers I cant help you with, ,nor the intake. One last thing, I seem to remember that the 5 speed overdrives from a military deuce and a half are supposed to bolt up to that bellhousing. __________________ 72 GMC C2500 402/Th400 first truck (still have) 77 GMC C3500 CC dually Sold 70 C50 dump truck "Rusty" 87 K10 Suburban Sold 93 K2500 xcab 6.5TD 96 GMC K2500 Suburban 6.5 TD

12-01-2014, 03:00 PM	#3
bdiamond Registered User Join Date: Sep 2007 Location: Wichita Falls, Texas Posts: 459	Re: 427 tall deck in a 1979 K25 GMC Unless you set the engine really high I bet you'll be hard pressed to find a pair of headers that fit inside the frame rails.

12-01-2014, 04:06 PM	#4
Puke160 Registered User Join Date: Nov 2014 Location: Paola, ks Posts: 42	Re: 427 tall deck in a 1979 K25 GMC If I use the MD transmission then I can't use my 205 transfer case because of the output shaft. I don't know about the military 5 speed. The truck spends 90 percent of its life in dirt, mud, or snow. I need the 4 wheel drive. And hooker make a set of headers of a standard big block swap in this truck. I call them twice, jegs, and summit and everyone I talked to said they don't know if they would fit. __________________ 1949 Chevy C3100 1979 GMC K25 1982 Chevy C20 2000 Chevy K2500 2002 Pontiac Trans Am

12-01-2014, 09:33 PM	#5
mrolds88 Registered User Join Date: Jul 2011 Location: WV Posts: 946	Re: 427 tall deck in a 1979 K25 GMC I totally missed the "K" part. Doh!!! You are right about the 5 speed. HOWEVER there may be an out for you. GM put SM465's in the big trucks with the 13" clutch. With that said, you may be able to simply swap the input shaft and be done. Or you may be able to swap output housing and output shaft onto the big truck 4 speed. That would do it for you. __________________ 72 GMC C2500 402/Th400 first truck (still have) 77 GMC C3500 CC dually Sold 70 C50 dump truck "Rusty" 87 K10 Suburban Sold 93 K2500 xcab 6.5TD 96 GMC K2500 Suburban 6.5 TD

12-02-2014, 01:07 AM	#6
Puke160 Registered User Join Date: Nov 2014 Location: Paola, ks Posts: 42	Re: 427 tall deck in a 1979 K25 GMC The truck has a sm465 in it but I think it's a 12" clutch not the 13" but if they useed the sm465 in the medium duty trucks it should be a pretty easy swap. It's coming out along with the np205 to be rebuilt and beefed up some. __________________ 1949 Chevy C3100 1979 GMC K25 1982 Chevy C20 2000 Chevy K2500 2002 Pontiac Trans Am

12-04-2014, 02:38 PM	#7
78maliburat Registered User Join Date: Jul 2009 Location: cleburne texas Posts: 174	Re: 427 tall deck in a 1979 K25 GMC I have a tall deck 427 in a 85 and jegs brand headers fit nice no issues



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