1956 Napco GMC

[Bo Duke]

I'm working on a truck for a guy I know. It titled as a 1956 GMC Napco 4x4. It's a 3/4 ton, with the rare Eaton HO front axle. He pulled it out of the junk yard, and there's a lot of mysteries on this thing. I'm trying to figure out what is original and what isn't. The truck is titled as a 1956 GMC, but he was told the original title was lost. I checked the ID tag inside he door, and at least the cab is a 1956 GMC

First- The VIN show's a factory V8. It does have an older V8 (has the script Chevrolet valve covers) but I haven't pulled the #'s from the block yet to see what it is for sure. I question it being a true factory V8 truck though, since it's a Napco (it seems like most conversions were straight 6's?) and the engine mounts are made of plate steel, welded to the frame. So either it's a old V8 swap, or the factory mounts failed at some point. Any other way to tell if this is the original cab and VIN plate?



Second- It has a Chevy hood and a GMC grill. The grill has has "100" on it, which I believe is 1/2 tons. So maybe someone swapped the front clip, and ended up with a Chevy hood?



Third- How can I tell if this is the original Transfer case? Are all these shims between the t-case and cross member factory? How about the 4wd shifter location in the cab? There's an un-used shifter hole up closer to the trans shifter. The T-Case has a name plate on it, but all I can really read is "Spicer" and 20x (last number isn't readable). I don't think this is a NP201 though.








And a couple random pics, since everyone loves pictures


Front axle

Lock out hubs

[blue 72 gmc 4x4]

First off I believe all GMC's these years came with pontiac motors in them. So if you have a chevy motor then its a swap. The original motor mount should be right under the timing cover and instead of there being mounts on the trans, the mounts were on the bellhousing. As for the 100 that means half ton.

[OrrieG]

Do some research here: http://www.napco4x4.org/history.htm

Transfer look right, but the front axle should have NAPCO cast into the tube next to the differential housing. Could be the front axle was swapped out at sometime.

[OKGMC4]

I'd have to look at mine (also 56 gmc) later today but I think mine says 140hp on the vin plate and it was a straight 6 hydramatic truck. I think the 180 hp is the pontiac V8. You have a chevy hood there as well.

[buggy5872]

Transfer case and front end appear to be correct. What do the lift blocks between the frame and rear end look like? They were special lift blocks and the u-bolt goes through 2 ears on the side of the lift block. Here is a pic of my transfer case for comparison

[northerngmc]

Originally Posted by blue 72 gmc 4x4

First off I believe all GMC's these years came with pontiac motors in them. So if you have a chevy motor then its a swap. The original motor mount should be right under the timing cover and instead of there being mounts on the trans, the mounts were on the bellhousing. As for the 100 that means half ton.

This may be true for US GMC Trucks but Canadian GMC trucks had Chevrolet engines, the same as Chevrolet trucks. So maybe it originated in Canada?

[1project2many]

GMC here in the US did use Pontiac powerplants. I owned a 56 for a while with an original 2bbl 316 CI engine. The Chevy V8 available in '56 was the 265 rated at 155 HP while the Pontiac / GMC "317" was rated at 180 hp. Judging by the door plate that truck was equipped with the Pontiac / GMC engine.

HTH

[72JimmyDiesel]

This truck looks to be slightly a bubba conversion. I'm judging it by the way the transfer case is hung. Napco used a bracket above the t-case that bolted to the crossmember. The data tag on line built napco's had a gvw of 400lbs greater than the 2wd trucks. It would read 7300 and also 100 were 1/2t and 150 would be a 3/4T. I have several Napcos.

[Bo Duke]

Thanks everyone, there's some good info here.

Originally Posted by OrrieG

Do some research here: http://www.napco4x4.org/history.htm

Transfer look right, but the front axle should have NAPCO cast into the tube next to the differential housing.

Thanks for the link, I'll check it out.
The front axle has Napco has onto it, on the drivers side.

Originally Posted by buggy5872

What do the lift blocks between the frame and rear end look like? They were special lift blocks and the u-bolt goes through 2 ears on the side of the lift block.

I don't have the truck here, and the pic I have of the lift block isn't very close up. The blocks do have bump stop pads cast into them.

Originally Posted by 72JimmyDiesel

This truck looks to be slightly a bubba conversion.

This is the direction I'm leaning. Luckily this won't be a full resto truck, so if it's not a true Napco, that's ok.

[buggy5872]

the transfer case has the correct napco mounting brackets. There are just a few extra spacers. It may be spaced down to get the correct drive shaft angles.

[dwcsr]

Its a GMC X series with a Pontiac 316 V8, made in Pontiac Mi. Long bed 3/4 ton #1045 off the line that year. Canadian GMC had a different ID plate that didn't say Pontiac Michigan, USA

The hubs are Dualmatic Twin-Lever locking hubs, period correct but not sure if they are vehicle correct. But they were an option on 3/4 and 1 ton with the HO72 axle.

I think you may have a more original drive line than you think.