really depends on type (i.e car, truck, airplane, heli, boat), scale, block size (Small Block/Big Block), and available room in the vehicle itself to determine what engine will fit.
iirc the engine is going to be too long and impact the rear shock tower so you would need a extended chassis big block conversion, thing people were swapping to the MGT spur back in the day, might have been putting a 32P CB on the big block and hoping it held up.
and they do make the 8.0 for the MGT, but i would not recommend anything past the .21 area, unless you are upgrading the drivetrain.
The easiest is to get an OS21TM. More power than the 3.3 and fits without any mods. Also expensive though.
Back in the day there were conversion kits for the t-maxx, but they are all long gone now. I had the XTM conversion kit. A buddy of mine had the dynamite. Both were for the 2.5 t-maxx. The kit included a longer chassis, chassis rails, center/outer cvd's, big block header and pipe.
I think the 3.3 t-maxx did extend the gap between the spur and rear tower, but I'm not sure it was enough to shoehorn a true big block in there.