Block cracked............. if only externally you can easily do a JBWeld repair. This is providing you do not have a closed cooling system. If you have a closed system it builds pressure which you don't have in a typical marine system and therefore a rec "jimmy fix" repair would be to have it welded.
Have you checked to see how far the damage goes????????
To answer the first question.....you can buy a reman 3.8 for about $1200....AND a 3.8L is a chevy v6 that omc used in front of a 800 series stringer drive