I just cracked a 454 out of a 89 force 235. Mechanical fuel pump. Two piece seal. How far back does this block go. It cannot be sleeved. Cracked almost to head bolts. Also, any ideas why it cracked? Piston in pieces, rod bent. I know water, but, from exhaust or head? 21 years old but well maintained. No salt water. Boat does (did) sixty empty. Any ideas for more efficiency and or power with realiability. I want to stay normaly asperiated. Also, four bolt vs. two bolt mains. Any help would be appreciated. First time rebuild for me. Can't believe this, broke in august!

That is a Mark IV block. It goes back to the late 60's. Any Gen IV block will work. You could also go to a Gen V or VI block and use your heads, but some of the accessories won't work. You will have to change the oil pan, timing cover, camshaft, etc. You MK IV heads will work on a Gen VI block. If you are going to buy another block, then you might as well go with a 502 and pick up some cubic inches. If you can build it yourself, then buy a block or a short block. If you can't build it, then you may be better off buying a takeout. A 500hp carb engine would be a really good upgrade.
Eddie