Bumping this old thread. I just went through the agony of breaking the seat T handle on my '69 40 and trying to find a replacement with no luck. (What range of years was this used?)
I had one broken and one complete, but I broke the good one when I pulled my seats out for the new upholstery. Doh!. Those t handles are super delicate.
Here's the good one before destruction:
I looked around for similar T handles kind of like what previous poster's did, but didn't find anything I liked. I definitely wanted something more durable and the round pull knobs posted make a lot of sense. I had already replaced my ramsey pto knob with a tear drop shaped phenolic knob and thought I might as well match it with round knobs for the seats.
I found a 35mm black phenolic knob on McMaster Carr with an M10x1.50 brass insert.
Used my M10x1.50 die to add some threads to the pull, worked great, and no more need for the set screw.
Hope this helps until someone makes a good repro cheap.