What are the main differences in the short block of the past (60s-80s) vs the named explorer gt-40p blocks ? ( if you took the heads off of them and just had the block and internals what are some of the differences?

I know of
cam gears
fuel eccentrics
and the two piece rear mains.

 

All 5.0 blocks cast after 1987 were roller ready with raised bosses in the lifter valley to accept the factory spider retainer assembly, and the lifter bores are slightly taller and machined flat on the top to accept the taller roller lifters and dogbone which prevents them from turning.

Some early blocks are a little heavier but it's not enough to make a significant difference in strength, none of the factory blocks are strong enough for high rpm(7000+) operation or blown/nitros builds in excess of about 450hp.