if you have one of each on the floor how can you tell them apart?

 

Look on the castings on the block on the back side (flex plate side). It will read 5.7 (means 350) or 5.0 (means 305). If you wanted to go even further get all the numbers on the block and by searching you can find out exactly what kind of block it is. There are alot of different generation 1 small block chevy engine blocks, but for us F-body guys I think the big change was in 87 for hyd roller cam setup.

 

Not all blocks are going to have the displacement stampings.

All blocks will, however, have the casting number, and that will tell you.

 

If the motors have the heads off you can just measure the bores. Under 4" = 305 over 4" = 350. However, not all 4" bore motors are 350's. That is where the casting numbers come into play.

www.mortec.com

 

Or if theres to much in the way to see the casting numbers on the back of the block, jack up the front of the car, look on the driver side of the bottom/front of the block and you will see 3 numbers; 638 or 627. Hope you have 638