Forget repair
I tried and failed to raise Mark Plastics over several weeks in early '06 so I repaired my '79 Hunter 27 fixed ports myself. I would not do it again. Hunter used very, very good adhesive to glue the plastic in the channel inside the two halves of the frame. I cut the lexan close to the frame, and then broke it out in small pieces with a pliers. It took a solid week. I put the ports back together with Dow Corning 795 sealant and JB Weld, but not quite leak free. Worse, I have crazing already on one of the trapezoidal ports, which have a gentle curve that I couldn't figure out how to replicate on the workbench. Considering the hours I invested, I would have better off fabricating new frames out of fiberglass or wood. I'll measure the tank for you tomorrow. Mine is strapped to the floor of the locker on the starboard side of the cockpit all the way to the front.