Either the RCPD built by Dan or the RC-monster from Mike.
Dan's kit is very nice looking. I haven't personally used it but the testimonies speak for themselves in the other thread. What I like about the RCPD (Dan) kit is that he provides a complete package with motor mount, batt mount, & ESC mount. Just bolt it in and go.
I personally am converting a ST-RR but I am going about it differently than most. I am using a RC-Monster motor mount but I am putting the motor at the front left position rather than the right rear. This allows me to keep my rear disc brake. I will use the speed control for front/overall braking but can add rear brake bias by mixing the brake servo. Ths setup will also allow me to run 2 2s batteries. One on each side of the rear drive shaft. This will let me use all of the lipos that I already own for 1/10th scale racing. I'll try to post some pics this weekend.
www.rcrcr.com --------> B-Mag free since fall '07