Okay so I was able to get my hands on a owners manual for the era of the boat (some revisions are '78) from Carvers archives.
The manual states to run both engines off just one battery, hence always having the other as a spare..... I'm not totally sold on that one. For one having 2 separate charging systems on the same circuit doesn't give me a warm fuzzy, I was having issues with one WAY over charging and that flowing through the whole system just isn't good. I did find the issue and some Genius at one point decided to put in a Chrysler single wire voltage regulator where the Pleasurecraft Ford model used to be . Also there is not a shore charging system onboard either so other then alternating between batteries on cruises there's not a reliable way to ensure charge. I'm planning on running each engine on its own battery for these reasons, if I'm way off I'm open to hearing it and appreciate others advice and knowledge.