Ok, I need some help. What are the differances between the Gen IV V VI motors and how can you tell which is which? A 500 HP Carbed Blue motor would be which Gen? Thanks for any input.

Get the block number off of it and check it that way to be sure.

A Mark IV has a place to mount a mechanical fuel pump on the engine block.
A Gen V has no place to mount a mech fuel pump and has a stamped steel timing chain cover.
A Gen VI has no place to mount a mech fuel pump and uses a cast timing cover.

Serial # check is the only sure way. Some GenVI do have fuel pump mount. Don't ask how I know.

That is true, but they do not have a lobe on the cam to run the fuel pump. That is why I had Bob Mandra help with cams.

Gen IV: Two piece rear main seal, fuel pump boss, flat tappet setup
Gen V: Went to one piece rear main seal
Gen VI: One piece rear main seal, hyd. roller cam setup using dogbones/spider to keep lifters straight in bores, lifters .300 inches taller than before. Used a front cam plate to keep cam from walking. No fuel pump provisions.

correct,the gen 6 blocks can be bored to 4.600,the gen 5 can only be bored to 4.530 safely,the gen 5 blocks all came with flat tappet lifters,all gen 6 blocks had hydraulic roller cams.