After a lot of research, I finally decided on an UltraShield road racing seat. I think the biggest reason is that the side bolsters appear to be a little bit smaller than the Kirkey's, which would make entry and exit a little bit easier.
I measured them the way Kirkey recommends, and also measured the width of the Clubmans I was replacing. It looked like a 16" would be a little bit snug, which was what I wanted.
It was hard to tell even by measuring, but it appeared that the Clubmans had a 20* lay back, so I ordered the same.
I initially installed it facing straight forward. It was an easy fit. . But the edge of the door was pushing into my upper arm. So I rotated the seat to be more parallel with the trans tunnel. And that's a much better fit.
I'm using Breeze seat mounts, which are angled at 6*. Coupled with 20* in the seat, I'v got 26* of lay back. I think that's too much. I'll change some spacers and see if I can make it more comfortable.
As you can see from the pictures, the 16" seat fits with plenty of room. I don't think you'de have any trouble getting a 17" seat in there either.
If your a tall guy, you could easily drop the seat to the floor. But then the shoulder bolsters would hit the door edge. The drag seat does not have shoulder bolsters.
I am surprised at how comfortable this seat is. I added a little extra padding at the bottom rear of the seat. Otherwise, the standard cover has plenty of padding in it. Easy to get in and out of. More room than a Clubman. And (I think) more comfortable than a Clubman.
I highly recommend the UltraShield seat. BUT... it took a long time to get here. Something like 5 weeks. You must be patient, Grasshopper.