OK, one member contacted me asking so I'll drop by once.
I didn't design this adapter, or come up with the idea. It is the work of Tim Kingsbury and George Asche Jr. They are AoK.
A number of years ago, they designed and sold quite a few of these adapter plates, maybe 50 to 100 is a couple batches. The design is sound, and the originals were very well made. There are pictures in Tim's blog showing them, and they looked beautiful.
Unfortunately, when George tried to get a few more made, due to demand, he had to find a new shop. That shop didn't do the same job the original shop did. The A833 side has the center hole too small, the bell housing side has the holes not located correctly or countersunk enough to keep the bolt heads from being proud.
Those holes must be precisely placed, or it just won't work. Using a CNC mill, you should easily be able to hold .0005 diametral tolerance, but unfortunately, they didn't.
The edges of the plates are even just saw cuts. I don't recommend them, and I wish that wasn't true. George is 93 and he only had this batch made because people asked him. I don't think he will offer them again and I don't blame him.
I'm going back to making my own. I was able to find via multiple sources enough information to get all the hole patterns correct, but the drawing I got for the bell side, didn't locate the holes up/down in relation to the center hole. I made a guess and had a sheet metal template made. It will bolt very precisely to either the trans or the bell, but on the bell the center hole is sitting .46 too low. I have to make an adjustment and then I'll do another template to test it.
Assuming I get it right, I'll do the actual plate. Mine will be 1/2 inch rather than .375 because I want the two top tapped holes to have more threads, and because it still give full engagement of the splines and the pilot bushing.
I don't mind helping people doing the swap, but I'm not posting in the thread anymore.
People who try to say something that, when built to the design drawing, won't work, when it has worked that many times just piss me off. Say it once, I get irked, go on and on about how the basic design is flawed, then you can kiss the rear end.