To try and make this necro less necro-y, I'm gonna contribute some advice.
I'd suggest staying away from metal at all, as it's hard to work with, expensive, heavy, and the original parts are Fiberglass or plastic.
Make full-size fiberglass parts and secure them using the ATV's stock bolts, in place of the existing panels. As for the wheels, contract an expert. That's a place you don't want to feurkh up. You may have to make an aluminum assembly for the brokeback seat if you want very hardcore replication. Also, for the lights, simply take the current system, and rig it in series to 2 headlamps, one for each side. LEDs won't work at this scale. I don't know enough about your rear lighting to give a good answer. Finally, the suspension will have to remain as-is, which limits your capabilities as far as recreating the Mongoose goes.
If you can keep up to your expectations, you'll have a great product yet.
