My garden tractor is a Simplicity 6216. The engine, a circa 1983,
verticle, 16 hp Briggs 404707 type 0145 has a bound up crank.

They don't make a replacement engine. I found a 18.5 hp Briggs 42A707
type 2238. Its a Vanguard(meaning commercial grade). It appears to be
identicle to the 402707 under the engine covers. The mounting hole are
a little off. Not knowing what I'm doing, I would guess that my
biggest worry would be matching the crank sizes where it drives the
belts. The pulleys need to be properly aligned.

Any ideas if this is a doable project?