Oh, well that makes it really easy! That's a LOT better access than most boats
I think either way is fine - plenty of boats have identical tanks so it's not like it's "out of the norm".
I guess the question is whether you like have that built-in "warning" that it's time to head back if you're far from shore by having the reserve tank.
In "my" opinion... If I ran identical tanks, I would plumb each engine to it's own tank. But I'd have a crossover in case one engine went down so the good engine can draw from either tank.
Another thought... why not have just one, extra large tank? It would be less expensive to make - but is there a downside? Granted, a little more cumbersome to install.
Another another thought... Moeller (and maybe others) makes large plastic fuel tanks. If you can find one (or two) of those that give you the capacity you want, I would do plastic in a heartbeat (as long the difference in price wasn't super crazy).
Anyways, those are just some thoughts!