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

[pfouts]

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

[rasorinc]

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

[gonzo]

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