You need to go by starter draw, not alternator supply. A typically alternator might be a 90A or less. Starter current draw in amps, is 200-300 amps.I think you are looking at 2ga at least, maybe 1/0ga.
not familiar with your boat, but there should be a few places to access trans and vdrive. remove the covers and look around in there. might help you find a good spot for it. just make sure you know what's behind the area your cutting out.
Been looking for a spot to place the battery without having to move it to far. There are a few spots, but nothing deep enough for the current battery.
I might just move it to the front of the locker. Would allow the my bags to fill more completely and be more to the rear of the boat then they currently are. And I could use the current wiring. Otherwise I'd probably need to run a 0 gauge wire to under the observer seat area.
I relocated both of mine underneath the little cubby hole with the two cup holders on the starboard side. I had to cut an access hole in the front of the starboard rear storage area. I was able to just pull the carpet up out of the way to cut the hole then lay the carpet back over the hole once I screwed the cut out piece back in. I'll shoot some pictures tomorrow and email them to you.
I did some more measuring if I order custom ballast bags from Wakemakers, I should be able to up my ballast weight to approx. 1200-1400 lbs. in the rear lockers and just move my battery to the front of the locker and maintain the factory wiring. I think that's what I'll do.
Trevor - I am interested to see how you got those under the cubby, sounds tricky.