Help! Identify i6 250 I bought!

[LoudLowNslow]

Hey guys, I have a 66 gmc that has an i6. The placard under the dash states its a 250. Here are the casting numbers on the engine in the truck


So I was at a swap meet today, guy selling a good engine out of a 66 Chevy pickup, same as mine, 3 on tree, stepside, 250 i6. I buy it, get home, notice differences
Casting numbers off new engine


Distributor setup on the original engine in my truck
Rear plate empty





Now, here's the distributor off the newly purchased engine. MUCH larger, and a different setup




From what I can tell, the carb. Is different, and the valve cover is even different. I'm bummed, how could two i6 250s both supposedly from 66, one from gmc and one from Chevy be so different? What the hell do I have here? Are parts interchangeable? Thanks for any helps guys.. -Paul
Posted via Mobile Device

[C10 - C90 Bill]

The "original" engine appears to be a '69 by the Date Code on the Block. The 2nd Engine appears to be much newer.

There is a "Pad" to the left of the Distributor. Let us have the numbers on that pad.

Bill

[LoudLowNslow]

Thanks for the reply, I will get those numbers tomorrow!
Posted via Mobile Device

[C10 - C90 Bill]

In the meantime, I checked on the Casting Numbers from the Blocks.

The 3921968 is from 1964-1976, which covers the '69 Date on the Block.

The 366855 is from 1966-1984. If all the parts on the newer engine are original, I would say that the engine is closer to 1984. I can see some kind of Date Code behind the dipstick on the newer engine, but it is not real clear to me. I see what could be an 8 or 9 (possibly '78 or '79).

Bill

[LoudLowNslow]

A pic I took earlier, of the new to me engine, by the dipstick


I will get pics tomorrow of the numbers by the dist.
Posted via Mobile Device

[C10 - C90 Bill]

The number is a 6. Most likely a 1976.

The numbers (and letters) on the Pad will tell us more.

Bill

[LoudLowNslow]

Thanks for the info Bill! I'll be sure to post the numbers and letters from the pad tomorrow night
Posted via Mobile Device

[LoudLowNslow]

Does anybody have a picture of the Pad by the distributor they has the casting numbers, I can't find them
Posted via Mobile Device

[awbrown]

You should pull the valve cover and see what the date is on the head ....Both casting numbers represent many years ,both are 250 casting numbers...From 75 up they had the intake cast into the head (integral head ) , but of course you can change heads easy enough...

[C10 - C90 Bill]

I can actually see the Pad in one of the pictures (older engine with the shot of the Distributor and Fuel Pump). It's to the left of the Distributor and right in front of the Fuel Pump. The numbers won't be raised, they are stamped. Clean the Pad good. Use a magnifying glass if necessary.

BTW, these are called the Engine Code numbers. It will include the Date as well as the Engine Suffix Code (actually a letter or letters), the more important ones in this case.

Bill