L88 was a 427 block LS 5 and 6 for hi hp 454 .if you want more cid out of the block you have a 496 498 are not hard to do. but you will not use much of the old 454 . sounds like you have a two piece rear main seal block so you want to use a block that your heads will fit. like oil pan all tin etc it needs to be a GM mark 4 block as well or the dart world or the newer cnc bowtie block. but not the marine 502 mark 5 or 6. with a seal adapter that will let you use your old crank in a one piece seal block mark 5 or 6 block but head s will not seal up on the new open deck