I have just done the after maket seat fitment using rpm brackets. I used the standard mounting points in my ute and it all worked out really well in the end. The drivers seat is now more central to the steering wheel than before and the seats also fit with a very large custom trans tunnel.
If you would like photos pm me with a number to txt as there is a few on my phone and id be Happy to have a chat about it.

Miata Seats fit real nice.

And yea, bolting the seats directly to the floor is probably not the best idea. You need some kind of pad or bracket to prevent the seat from ripping through the floor. Similar to how the seat belts are anchored.
You can probably have new brackets fabricated and welded to the stock postions or maybe a bar or bracket that goes all the way across from the trans to the side rail.

At this point, you may want to wait until you find some seats before you fab anything up.

There are two B110s in Bay Area wrecking yards. Were you able to find the brackets?

Thanks or the replies!
And I was not able to find anything. I called ahead first and the one I found could not be located on the pick n pull system.

Still got a coupe shell here with the brackets if your keen can post them with the shifter if you want it. Again if your happy to pay for the items and post.

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That would be wonderful if you could part out those brackets and shifter!
How much would it run me shipped to California?

Would it make a difference that they are RHD?

I doubt if RHD and LHD are different for sheet-metal brackets B & C. They are spot welded to the floor.

Oh I see, so It shouldn't matter then. Thanks for all the help guys. This community is very helpful unlike others. Lol!