Driveline ID question

[tls3028]

Just got ahold of a 40 convertible w/ a 51 merc EAB head engine with 5/8" belts and 4 blade fan. Thus not real sure of what the engine is. Has the left rear oil filter canister. My main question today is transmission oriented. Will the trans and rear end be changed due to the later model engine being utilized? I read where the bellhousing is no longer attached on the 49-53 flatheads. I am needing to order some transmission parts. New 2nd syncro and other misc. Some input would be nice.