You worked hard on those rims. You should be able to reuse them, however, this gets to the original problem of finding 2.0" tires.
Ilooked online at Stormer Hobbies and found 2" rear tires https://www.ssl-stormerhobbies.com/c...s&pn=LOSA7378S
. This was the ONLY set I cound find so, grabbing at least 1 pair might be worth doing. Ihave the same set on the rear of my RC10. If you cleaned your rear wheels well enough then you could glue a set of these on there and be one big step closer to running brushless. Using these tires also means that you wouldn't have to swap out your axles and drive shafts, yet.
I couldn't find a set of new 2.0" front buggy tires but, all is not lost as you can still mount B4 rims on the RC10. You will need 4 new B4 front wheel bearings beause the old RC10 bearings are flanged and will stick out too far on the wider B4 wheel, thus causing the wheel nut to clamp too tight against the bearings.
Even after all this, you should still swap the 6-gear tranny for a Stealth tranny. Here's an example Ifound on eBay: http://cgi.ebay.com/Vintage-Associat...item20bada9e83
The price seems right and it's actually from the RC10 era. I wouldn't dish out more than $50 -$60 for one.
You've quite a task on your hands. Not impossible but this will take some effort. It's up to you to decide whether retrofitting is worth it or starting from scratch with a modern platform will be more reasonable. Consider which route would give you the greatest satisfaction and go with your gut.