Use the original brackets. Just like that.
Miata Seat Brackets - Google Photos Album

RedRiley - in another post about the making of these brackets, you mentioned toward the end of the explanation, "once it's bolted (the newly made frame) back onto the seat, it pops onto the stock seat brackets and functions exactly like the stock seat"... are you saying that the newly built frame is to go back onto the stock mini seat frame? Or does the new setup bolt directly where the stock setup goes?

Thanks for the comments Scargo and Bill and for the terrific pictures Brian.  Very helpful.

Jack

Jack,
Sorry about the email not working. Old email that apparently will NEVER be allowed to be changed. I don't get it. How hard could it be to fix that?

Anyway, it's not super complicated. It's essentially just copying the Mini seat brackets using the Miata parts. Basically you just need to tie the two seat runner brackets together with a cross bar front and rear, then make some provision for legs or height adjusters at the rear, and some attachment points at the front. 
Here's a link to some photos.

scargo.. same way I did my metro seats in my mini.. tons of leg room... later bc

This doesn't satisfy your request, but I mounted my Miata seats directly to the floor pans, behind the cross member and without the use of subframes. The result is a very low seating position with gobs of front leg room. What some might consider to be a downside with this arrangement, is the inability to slide the seats fore and aft, and the lack of rear seat access and legroom, but none of those are concerns of mine.

I have a real nice set of Mazda Miata MX5 seats that I want to install in my '84 saloon and was wondering if anyone had a picture of the seat frames that have been used for this purpose in the past.  I know Red Riley had/has a set in his Riley by I haven't been able to contact him through the email listed in his profile.

Thanks.