I made a rowing rig for my 16' MR Explorer 40 years ago.
I made it like a clamp-on portage thwart with screw knobs and L-clamps, except it was straight and extended several inches beyond the gunwales. I had a drill then, and drilled holes in the ends for for oar locks. I had Carlisle Paddles make me two paddles with button-push removable grips that could be replaced by long oar handles. Clamping the rig on the gunwales, I could row from the wide center seat I had installed in the canoe. I had gotten the dimensions for the rowing thwart and oar lengths from some rowing source, and it all worked okay.
I also had Carlisle make me a long center section of tubing that could button-clip onto the two oar sections, creating a 12' pole. Therefore, I could travel with five Carlisle sections that could make either two paddles, two oars or one long pole, plus my clamp-on oar lock thwart. Very compact, and I doubt the entire thing cost me $100 dollars in those days.
Until I began hating the Herculean heft of Carlisle paddles. Then, I switched to wood paddles and lost interest in the rowing rig. The pole remained useful but I can no longer find the constituent parts in my hopeless cathedral of entropy.