I was hangin out with some rednecks last night, and I popped my hood and one of them said it looks like I have a 305. I was told I have a 350 by the PO.
So is there a way to identify the difference? If it means anything its a '78 3/4 ton and it has a 4 barrel carb.

 

not a good visible way with out getting the id number off the passenger side flat pad on the block or casting number off the block drivers side bellhousing flange of the block .

 

Does it still have the emmission sticker?
It should tell you either 5.0 or 5.7

 

Checking the block for the casting number would probably be your best bet (as mentioned by old dog), especially if it was swapped out previously (wreck, just wanted to, etc...) If it is an original engine, and the emissions decal has fallen off, check the VIN through the windshield on the drivers side dash board. OR it may be riveted on in the drivers door area by the striker bolt. There was a transition between the door and the dash board location.

Here some info I found at http://www.chuckschevytruckpages.com/73-87specs.html

Engine Designation:

R = V8-400-4BBL
L = V8-350-4BBL
U = V8-305-2BBL

So it appears to be a 350 (4BBL), but check the letter to make sure (looks like the 3rd character).

 

I sure hope your redneck friend is right, 305s and 350s are the same engine family, and SHOULD look like each other, it's the same engine block. You should be able to find the drivetrain info on the RPO sticker in the glovebox. (Assuming the drivetrain is original)

It's a natural assumption that a '78- 3/4 ton pickup truck should have come from the factory with a 350. Do your redneck friends know of a special 3/4 ton model pickup of that year with a 4 barrel carb that had a 305 engine? Maybe a mid-year change that GM only told them about?

 

I was thinking the same thing. Aren't 305's up to 400's all small blocks? The difference is the pistons, crank, and rods?
The PO told me it was rebuilt. But didn't say anything about replacing.
I'll check my VIN

 

if its a 3/4 ton, its most likely a 350. thats usually what they put in the bigger trucks. unless it was a big block.

 

"Rebuilt" is a real grey term. That could be anything from just replacing the head gaskets to
removing the whole engine and replacing it with a new short-block. With about a million variations in-between. If you know the PO, he should be able to point you in the right direction.

The funny thing is, because of supply and demand, more than likely any replacement engine installed in the truck would be a 350, because they're cheaper and easier to find than 305s.

In any event, if the rebuild was done without removing the engine from the truck, I think it's safe to say your engine's displacement is at least 350 Cu. In.

 

here is some info if you check you casting or id numbers .check out this site .
http://www.nastyz28.com/sbchevy/sblock.php