Specifically, you never mix batteries of different capacities, chemistries or age to form a single bank as it creates battery charging problems and tends to reduce the lifespan of ALL batteries in the bank. So kids, don't try this at home. (In this case, I don't care if I shorten the life of these batteries as they were used and had been taking up valuable space in the garage anyway.)
Another part of this exercise is determining the best route for the big cables that lead from the battery box (under the center forward floorboard in the main salon) to the engine room. The initial plan is that the cables will be routed above the floorboards, through 2 inch conduit following the outer inside perimeter of the dinette riser of the main salon.