Hi Mark i'm not a V8 specialist by a long way but unless you are using a full race cam with massive overlap I would of expected compression pressures in the 120 to 175 psi ranges 80 sounds like the engine is turning over to slowly or you aren't holding the throttle open fully to let the air in when cranking.
Also if you are using a dual point distributor it's easy to time the dizzy up the the wrong cam lobe heel, and a lot of people time the dizzy up statically to the wrong side of the dizzy cam lobe i.e thinking the dizzy shaft turns the wrong way hence setting the opening up well after the correct time, often when they are set this way they don't even cough and spit. If as you say you are a novice builder it is probably only one of these stupidly small detail things that aren't quite right.
Hope there is a little bit of info here that may help, if you are using hydraulic tappets you have to have a very gentle feel when feeling for the initial contact of the push rods to lifter cup and rocker arm seat. I always very gently hold the push rod very lightly between thumb and forefinger lifting it up and down a few thou and rotating it gently to feel the initial friction you get when the clearance is just taken up, then if my memoryserves me correctly you then give the adjuster a 1/4 or 1/2 turn (depending on manufacturer) of pre load. You don't normally get a lot of compression on the lifter cup so you can easily over adjust the initial setting when the lifters are empty.
Hope you don't think i'm sticking my 4 cylinder nose into your problem but I think an engine is an engine.
Good luck John