It is easier to just put a OS TZ .18 in instead. You are gonna have a hard enough time getting the car to hook up with that motor . I had a .21 Hyper -8 port in my nitro TC-3 and all it did was spin out.
I believe the adage "You can never have too much power" might ultimately be defeated in this scenario. I figure you'd just nuke the tranny before you even got a lap in, and it'd handle like crap with that kind of extra weight above the center of gravity.
Putting .21's in 1/10 tcs is common-place in the Chicagoland area. There is a group of run what you brung style drag racers that have been doing that for years. For the most part, the trannies hold up pretty well. Easiest conversion I have done was LD3 rtr. .21's drop in with no conversion necessary. Just add buggy header.