It is a big deal if you are trying to use the exact same stringer holes.
My crummy old small blocks use the front motor mounts, I'm assuming this is the same as any truck or car, surely putting an LS motor in your jet boat would be the same Paul. If they don't line up you can always just drill new holes in the block to line up with the ones in the stringer anyway? Dave is installing a Cummins in his boat, that's gotta be about the same so what's your problem? My guess is you just didn't bother to do any research on this.