You can use the stock transmission crossmember in the mazda just need to weld holes shut and then redrill about 1/4 forward. As for motor mounts, jegs sell a set of tubed V8 mounts that take old GMC truck style mounts you just bolt onto motor lower it down until tubes hit topside of frame. Mark off and cut so they will slide down between frame rails. After that just weld in. Really really simple.
I made my own mounts out of 2x2 box tubing and steel plate, but they now have tons of universal mounts in Jegs/Summit racing catalog.