Can yours be rebuilt? If not go with a short block and have your heads re-done if they are any good. Are you going to do the work? In years past we have taken an automotive engine and turned it in to a marine engine by putting all brass freeze plugs in and marine head gaskets.
try doug russell marine. we used them once found them to be good to work with. they ship everywhere and usually have a number of options available. good luck
I just did two reman 7.4 longblocks (same 12 month warranty as new) from Michigan Motorz ( www.michiganmotorz.com).
Just splashed her yesterday, so not much time on them, but I was very happy with them, their pricing, and service.
Think they have Gen IV's (mech fuel pump?) but I got the Gen VI's and converted to electric.