There is also the Forward Tranny TVPs from FLM, bit pricey at 185. But no need to customize anything.
I'd skip the HPI kit, rather go with the Flux TVPs from TCS as you can get them really cheap if you want standard length. And RC-MONSTER sells them.
Also you can get a drilled out HPI clamp from GCM racing.
Trannys are pretty cheap on eBay. Just get the HD 18-23 drive gear (
http://www.tcscrawlers.com/HPI-HD-DR...4-p-17468.html) for it.
Do some searching here there were a couple of outrunner conversions do with Savages that were posted.