How much HP is your son planning on making with his rotary? If over 300HP is the plan then a 13B with some serious bridge porting or even a peripheral port engine is required, for durability I would go for the peripheral port engine and fuel inject it. As for transaxles I would look toward Xtrac
for some heavy duty manual transaxles. These are the same transaxles used in the British and German Touring car championships racing series and can handle some real abuse (Best d@mn racing on the planet BTW!).
It is going to cost like the dickens though.