I posted the same suggestion a few years ago after test-fitting a seat from my own 1990 (1st year) Miata in my inactive, final-year 544. The seat is lightweight, fits with lots of room to spare, and is of foam-padded, sheet metal pan construction of durability, comfort, and abundant lateral support. It has much less vertical height between its mounting rails and tush level, so there is plenty of room for adapter arrangements (which I did not design or build) above the 544's built-in seat-carrying structure. More vertical footroom or stowage height under the front seats would thus be obtained. A bonus the Miata can't use but the 544 can is the Miata seat's generous reclining provisions that are combined with its side lever-operated backrest angle adjustment that backseat passengers would need to use to get in/out.

Miata integral headrests had/(stillhave?) provisions for optional speakers in them; mine didn't have them installed and member John Mc commented back then that those speakers are not very powerful. A deeper bucket shape in the seatback is easily obtained by slipping out the 2-inch thick foam pad from the lower center section and carving a tapered transition in the upper foam padding with a sharp kitchen carving knife. I did that in 1992 upon buying the Miata to get myself enough leg room and I still enjoy the more surrounding backrest fit to my rounded ribcage that resulted.