Hi Ben,
When the two sails are of equal size, the mast positions are a little further aft than with the PJR recommended proportion of 33/67% fore/main areas. Thus, the after mast is somewhere about 60% of the waterline aft, and is likely to go in the position you need, just forward of the galley. Bear in mind that it can be offset a little from the centreline, to ease passage around it. The foremast is likely to go a little aft of the watertight bulkhead at the forward end of the waterline, so that will be convenient, too. I favour two equal size sails, where practicable, for convenience when sailmaking, carrying spare battens, and running wing and wing.
5.5oz/sq yd sailcloth is a bit too light for this size of boat and sail. I'd recommend 7 to 8 oz/sq yd. My experience of the light weights of Dacron cloth is that they don't have much UV resistance, so need to be kept covered when not in use ( unless there's still any Haywards "Sunwing" cloth still on the market - that's UV-protected). I would say that the best cloth for your sails would be Mustang/Top Gun 9 - if you get 100 yards from
Rochford Supply, it will cost you $9 a yard, and you'd use most of it, taking into account a finished sail area of about 800 sq ft, plus pockets, doublers and tablings; and then sail covers, mast coats, cockpit awning, etc.