I bought my 16' Domar bucket boat new in 87. My chief bailer was usually my long-suffering very petite wife. About 15 years later, she had had surgeries on a neck vertebrae and rotator cuff and discovered that most of our boating friends had self-bailers. At the time we were living in Anchorage, Alaska. I had a friend at Alaska Raft and Kayak, Tracey Harmon, who is a fantastic raft glue guy. He knew someone in Eugene, Oregon who fabricated custom SB floors. I wish I could remember that guy's name. Tracey took the old floor out of my boat and shipped it to Oregon. A new grommet-style SB floor was fabricated using the exact dimensions. Tracey professionally glued in the new floor perfectly. The boat tracks like it came out of the factory that way. Total cost was $1800. I have no idea if there is now anyone around that could do it this way or how much it would cost in today's dollars. But it was worth every penny at the time. I still have that boat and it is in great shape.
That said, my trips in Grand Canyon have all been in 18' bucket boats. Have to admit, I have been full of water a couple of times and might have flipped without the extra water weight. On the other hand, maybe I could have avoided those holes altogether without the water weight slowing down my ability to ferry the boat over.
It didn't take much rowing to decide the SB feature is worthwhile for the oarsman as well as the bailers. If you are trying to make the move to avoid Skull hole in Westwater or maneuver through Snaggletooth, 1 or 2 people with buckets can't lighten your load near fast enough. I loved the SB immediately and will never go back to a bucket boat except for flat water fishing.
So I would vote for conversion that is done right. I just don't know if a truly professional customized conversion is even available anywhere right now. Even if it is, only you can decide if the old boat is worth spending that much money on.