What do you intend to do with it?
For the most part, 454’s are the same from 1970-1990 & they are considered Mark IV. Most everything interchanges between all years. The Mark IV has a 2 piece rear main seal & the later ones have weak cranks. Mine is a 1990 & the crank & 1 piston broke when it had 26K miles on it. The last 2 or 3 years of the Mark IV production motors were junk (Brian will tell you all BBC’s are junk).
1991 & up production 454’s are Mark V & do not have a provision for mechanical fuel pump. Also have 1pc rear main seal & many other small changes. Some issues can occur if putting Mark IV components on Mark V blocks. Not impossible, though. The aftermarket has supported the Mark V pretty well.
The Mark VI has all the benefits of the Mark V plus a mechanical fuel pump boss. I am not positive if there ever was a Mark VI ‘production’ 454ci block. I think the 496 (8.1L) are all Mark VI. Brian can probably confirm this.
That 496 short block is a steal for $500.