Depends on what you want. M112 is the same engine in Merc-speak so should be a near bolt in. M113 is V8 version and have been many conversions. At least around here, both are plentiful. M272 is a DOHC version but would avoid any prior to late 2007. Buick 3800 was used longitudinally in Firebird , is a 60 degree V6, and L67s make A Lot of power.


So the real question is "how much power do you want and how much work is acceptable ? (can substitute cubic money for effort).