Well, Im not sure what other manufacturers make, but the 3R uses 0.8m which is a finer pitch than the 2R - more teeth per unit of length if that makes any sense. I don't see why you cant use the RRR clutch unit that holds the pinions, or just use the pinions from the RRR on your clutchbell, but you should make sure the spurs and pinions will be able to fit onto your car.
So far Ive only been using the Kyosho gears, but recently I bought myself some 3Racing spurs, and the comparing the two brands here is what I found:

56t:
Kyosho - 18-19g
3Racing - 10-11g

61t:
Kyosho - 6-7g
3Racing - 5g

So they are fairly light, but I don't know how durable they actually are!