I hope not the fence post t-clamps. Uggh!
(they're ugly and rough. Try to find Speedrail fittings that fit your fence posts, or weld select joints.)
Electrical EMT conduit and fence posts/rails are often 1/8" different in diameter, so you usually can find one that will snugly sleeve in/outside the other. You can find pre-bent conduit elbows.
Refer to Chip's frame thread for details.
Go to Harbor Freight and pick up the Storehouse box of PTO pins. Much cheaper than buying them individually....and even if you buy them individually, they're still made in China or India. 20 Piece PTO Pin Assortment
Unless your fence posts are exactly 1 5/8" OD, you can slip a piece of PVC or hypalon (raft repair fabric, or if you know a commercial roofer, ask them for a scrap of roofing material) between the frame rail and oar tower.
Have fun and post some pics!