if my memory serves me correctly, and what i have read is right, the first ones that stuffed the renesis engine in a miata, was Mazda themselfes actually
Back before the rx8-thought was conseived, Ford was much heavier into Mazda then now. When Mazda engineers approached Ford execs with the thought of developing and building a new RX car, they were "shut down" by Ford, probably due to Ford not wanting a competitor to their sportier vehicles....
Mazda engineers and Mazda HQ in japan took this very personally, as the rotary engine allways has been a very dear consept to them.
Mazda engineers started an "undercover" project, and used much of their free time and own time(after work hours) to develop the renesis engine.
They stuffed the renesis-consept into a miata(chassis-wise close to what they pictured as a lightweight sportscar,with a 13B N/A engine) and shipped it to Ford HQ to let the execs have a go in it, and they were blown away by it and freed up the funds to develop the RX-8.