That's exactly like my PAC 1000 frame. Mine's about 15 years old now, but going strong. My seat slides on those rails for adjustment. I didn't like that a hefty push in a rapid made the seat move on the rails, so I bolted the seat in place. I'm sure you can figure out a mounting system for a better seat. Looks like you already have decent open oarlocks, so that's good. I would call the folks at Outcast and talk with them about seat ideas. The D-rings on mine got a bit rusty too, but they clean up ok. Are the tubes in good shape? Hold air good? Those tubes are 18 inch diameter, so you'll be up out of the water higher than most pontoon fishing boats. With a little work, you'll have a really nice little boat. You are going to have so much fun !!!!!!
PS - Oarsman - OK
Oar rig - OK
Crap I busted my oar - OK
I love being on the oars - OK
I'm oaring my raft down the river -not so much