I have a 1977 400 out of a donor truck that my dad had bought a couple of years ago. The guy that he had bought it from said that it was "built". It has an edelbrock carb, intake, and valve pan covers.

I pulled the oil pan off to verify the casting numbers on the crank and it is a 400. So how do I tell what all was done to it without doing a complete teardown? I should be able to mic the cylinders to see if it was bored, but what size is factory? Can I verify the cam without pulling it?

 

.
. May be able to mount a dial micrometer via magnet mount inside the engine, turn engine over, and measure the lobe lifts on the cam and get a good estimate of what it is...

. Using an inside caliper inside the bottom of the cylinder bore, discover the bore size... stock is 4.000" for 351M/5.8L, 400"/6.6L, 351C, 351W/5.8L, 302"/5.0L, and 352"...

. Pistons, hard to tell, maybe a bore scope TV camera would let you see the top of the piston... see if dished, flat, or domed...

. Cpmpression test to see if around 125 psi, 175 psi, 225 psi, etc...

. Driving test... power from 1000-4500 RPMs, 2000-5500, RPMs, 2500-6500 RPMs? Give an idea of cam size...

 

I found out that it's a jenkin's rebuild. They take original engines, rebuild and fix any issues and sell them as a crate engine. Has 28K on it. Not sure exactly if it was modified though, but I'll run it (if I ever get the truck finished) and see how it goes.

 

.
You could pull one head, take off one rod cap, pull one piston and see what it is... that would give about all the info there is to know... (along with the cam info above)