Here's a clip from associated's website for the NTC3.

Rear or side exhaust engine compatible, excluding big block. Manifold and pipe included. Standard short shaft or SG crank shaft recommended.

http://www.rc10.com/shusting/Catalog...c3/kitntc3.htm

I'd go with the cheapest slide valve engine they have. The short shaft will fit. If you cut some of the threads off the standard shaft, it will fit. They also indicate that the SG or pilot shaft engine will fit.

Good luck