Yes but Its cheap to buy a new short block with out carb $65,
I suspect you are having tuning problems with the carb? This always happens and the easiest fix is a fuel filter and cleaning out the carb. Traxxas never includes fuel filters in any nitro kit.
If you can find a small block with pull-start, rear exhaust and a slide carb, it would fit. You may need to figure out a new clutch/clutch nut/pilot shaft and will likely need a different exhaust header as traxxas's is proprietary that doesn't fit anything but traxxas engines.