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
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