There's a thread on the Triumph & 6-Pack Mail Lists about producing brackets for a TR6. The two guys doing this are vintage racers: Joe Alexander and Jack Drews. Here's the email:
"The recent activity on this subject seems to beg for a bracket design, so more Miata seats can be adapted to the TR6s...and I presume TR4s, too.
There's a couple of retired John Deere manufacturing guys who do this kind of thing. One is 'Uncle Jack'. He has a very nice TR6 with Miata Seats. I talked to him today and asked him if he would be interested in this as a project.
It seems very worthwhile for the Triumph Community. He was enthusiastic about the idea
Jack can design it based on what he has now and improve further on it. My son can finalize the drawings for best manufacturability, then schedule for production on CNC equipment. They likely could produce 25-50 sets very economically....if there is enough advance interest.
Jack is off to New York for a wedding, but will return shortly. NFI on my part. I just think it is a good idea.
Who's interested? I'll copy Jack here, so include a reply to Jack."