Obviously, the masses are gonna tell ya to dump the Olds and go with a Chebbie or a Ferd. I have all three. To be honest, no real difference in "marine" form. Real difference is in "Hot-Rodding" them where the others lend themselves to more handily.
As far as converting from one to another? If you love the hull, or it's worth it, then yeah. But it ain't cheap and ain't easy. Nordie did it to change from a Ferd to a Chebbie..........I think he'd sooner stick his junk in a beehive than do THAT again..........
Pull the momo, pull it apart and see what you smoked. Probably a rod bearing or two, the white smoke, to me, would indicate valve issues or maybe you stuck a piston. Block full of sand, who knows until you get it apart........

........I'm a firm beleiver in not doing anything to fix nothing unless you know WHY it failed to begin with.

Ray