For the bigger ones I like the Thunder Tiger Bushmaster but you don't have a good place to run it.
Yes, you'll need to get both the spur and pinion.
I just replaced mine and it was more work than it should be. I counted 25 screws to get to the spur gear. Maybe I went about it wrong but I had to take off the whole rear end. The back wing was in the way of the rear diff case screws so that had to be removed too. Unnecessary for it to be so complicated.
I put in a 58t spur (60t stock) and I couldn't get a 15 or 16 tooth pinion to work without modifying the motor mount. 58/14 is what I ended up with. I haven't run it yet. I'm going to change the shock oil to 20wt.
Tekno SCT 410.3, Arrma Kraton, Traxxas Slash 4x4, Tacon/LC Racing Rally/SCT/MT x3, Losi Mini 8ight, Carisma M10DB, Axial AX10 Deadbolt, Vaterra Ascender '72 Bronco, Thunder Tiger Kaiser XS, Sky RC SR5 Super Rider