They don’t make an engine mount for a standard short or extended stock TMaxx chassis for a true BB engine.
You will want/need an aftermarket extended chassis or a chassis extension like a mono block or custom made top plate/skid extension to mount a BB engine properly.
Any other way you try to mount a BB engine on a stock TMaxx chassis will just end up as a chop job and not last very long or look good.
The footprint of a BB engine is not only wider it is much longer than a SB engine. The snout/nose of the engine is longer on a BB and thus you have to move the engine backwards on the chassis in order for the clutch/bell assembly to mesh with the spur. When you move it backwards the starter assembly (either, pull/Roto/EZ start) will then hit the lower portion of the rear bulkheads and not sit level with the chassis deck. The headers needed for a BB engine are larger with less of a bend than a stock or SB header and it interferes/hits the the shock tower causing issues.
I could go on, and on but you get the point. An aftermarket extended chassis designed for a BB, or a custom extension added to the chassis with an extended rear skid plate or a mono block extension is the best way to go about it.