360 marine cranks?

if it is the reverse driven side, I thought I read somewhere that the area where the rear main seal rides is different. stock cam?
It had a stock replacement cam previous owner rebuilt then I put an old crane energizer cam in I have and different timing chain. Has compression fuel and spark. Wont even fire or sneeze like if I was 180 off. And when I hold throttle open it sounds like one or 2 cylinder push air back out like valve events and pistons are out of cycle with each other.