1989 4.3L - upgrade to 5.7 or newer 4.3L questions

I have a 1989 Ebbtide Rivera with a 4.3L engine with a cracked block . I would prefer to upgrade to a 5.7L and if that is not possible, to upgrade to a newer 4.3L Vortec long block.
I believe I have enough room for the 5.7L - however anyone know the difference in length of the block?
Since the boat has fixed motor mounts, does the 5.7L block have mount locations anywhere near the 4.3L ?
And if the 5.7L is not possible, anyone know of issues replacing a 89 4.3L with a newer vortec - that way I can have a smoother engine and there seem to be some upgrade options with 4bbl manifolds available for the vortec engines.

Thanks for any suggestions,
Pat

 

This site will show you all necessary dimensions of the GM engines. http://www.gm.com/experience/technology/gmpowertrain/engines/specialized/marine/marine_engines.jsp No problem changing older 4.3 to newer 4.3 though I cannot say if GM changed the motor mounts--it's doutful in my opinion. Newer ones come with fuel injection.
Check out Michigan motorz http://www.michiganmotorz.com/marine-engines-partial-engine-packages-c-31_55.html

 

If you change the engine to a 5.7, you will have to re-gear the transmission too.