here is the problem;
The centerline of the crankshaft, where the flywheel will be attached and the drive genrated from, on a recip piston engine is in the lowest point of the block, whereas on a rotary engine this is in the middle. The problem then becomes making the trans fit through the firewall which either involves cutting or making a new subframe/engine mount that will likely be non streetable because of oil pan clearance issures. I would love to see it be able to be easily swapped as my g/f miata would be fast with a cosmo 13btt : )
There is a co. in Au that sells a complete subframe, weld in 1/2 chassis style, swap for 1st gen miata's to convert to the Fc 13b T, can even get the hood for intercooler complete with T2 scoop. Good luck and keep dreaming. It's good for you : )