I have a Larson 186 SEI that was repowered with a 350 Mag Alpha One Gen 2 (I think it was originally powered with a Volvo Penta 4.3L before I got it.) That 176 will easily handle a 5.0L engine.
The 'front motor mounts' that chevymaher refers to are (I think) what you are calling "side mounts"; on a V8, there are the transom mounts (rear mounts) and the front mounts (which are on the side) and are usually fiberglassed to the stringers. I believe chevymaher is correct that the front mounts for the SBC are located in different spot than those for the 4.3L. My buddy has a 4.3L and his front mounts look to be about 3-4" closer to the transom that are the mounts for my V8 (I believe the blocks for the 5.0/5.7/350 Mag are all the same). I don't know if the 176 had a V8 as an option when it was new, but if it did, the mounts may already be set to receive a V8 and installing the 5.0 would simply be a matter of drilling new holes for the front mounts (and filling the old ones).
I like your idea of using the 176 as a recipient of your engine/drive. Being a 2000, the Larson would not have wood stringers, so your chances of getting a boat with rot are much less. I don't know if they were still using a wood transom core in 2000, so check that very carefully, especially around the keyhole and the ladder thru-bolts (the latter are notorious in Larsons for leaking and causing the transom to rot). I'd bring a screwdriver and try to turn the ladder screws. If they are loose, look carefully for rot.
I don't know if a new harness would be required when dropping in a 5.0; mine looks like there was quite a bit of new wiring from when the motors were switched. That's a question for some of the others here to answer.
Good luck, looks like an interesting project.