The RX7 is a 4 link setup, and the wagon is a leaf spring setup. Not that this is an insurmountable obstacle, but it's a bit involved.
The one thing I've noticed with the 510 wagons is that the floor pan is too low to allow for decent suspension travel, especially when the rear is lowered a lot. If I were doing up a 510 I'd find a sedan, but if you really wanted a wagon I'd cut out the floor and allow room for the axle to have a reasonable degree of bump travel, then I'd do circle track style sliders instead of rear shackles, then if you're putting down a whole bunch of power some generic traction bars.
I tried to convince my friends to do this on theirs, but no luck so far...