You might hit up some desert-buggy sites for motor input. There is a class limiting the motor to stock specs (similar to IT) that has been around for decades. There's probably a bunch of wisdom there.

For wheels, the porsche 914 fuchs (4-spoke, not the 5-spoke like on a 911) are plentiful, cheap and light.

I used to auto-x a beetle and had a blast. I've often considered an IT super. I'll be watching this thread!