TOPIC: cross reference info, swap lower units & weights,

Are there sites that I can use to cross reference swapping out sections of motors, the lower units,
example :
i have a mercury 350 serial # 2089974, if someone has a 1837996 would those lower units be compatible to swap out?

Also, can i find info on the weights of motors for shipping to purposes if i just want to buy a engine. somone has a 1960's mercury 500 i'd like to know the weight for getting a shipping quote. or maybe aprox weight
THANK YOU