Possibly the best thing to do is find a car on eBay or whatever to use as spares, I think the bargain bin is the only place to find unused spares for the Pro 2.
The bulkheads from these kits will fit:
Nitro & Nitro 2
Super Nitro, Super Nitro Rally, Super Electric
Sport, Sport 2, Pro, Pro 2 (obviously)
The Pro 3 bulkheads are entirely different, so are the Pro 4 parts.
The suspension arms from the Nitro, Sport, Sprint, & Pro cars will fit, you might have to use spacers on the hingepins or do some hand-fitting but they all use 3mm hinge pins.
I hope this gets you started off OK, the Pro 2 is still a legend, very tough and plenty of fun!
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