Big Red Engine Swap?

[Excal]

Will the 250sx engine fit in my big red 250es?I got it for cheap and the engine is junked(locked up).
So what engines(wholes engine,tranny and all) from what OTHER models can I just ''bolt in'' and ride?

[atc350xer]

The 250es and 250sx are direct swaps, but the gearing is a bit taller in the sx. The '86-'87 swing arms/brakes are different from '85 in both machines. Also, the TRX250 quads from the mid 80's have the same motor, tranny, and swinger as the Big Red.

[TheRealFatShady]

Additionally, you can use the TRX300 2wd engine (1988-2000) you just need to swap the output shaft from the big red junk engine.