[Eddie49]

... and if the input shaft doesn't need support at the end... you could cut off much of the protruding shaft length and build a coupler which goes onto the remaining splines, reducing the length of the housing and how far back the motor must sit.

The great length of the non-splined part of the transaxle input shaft suggests that it does need support - presumably from a very long or very deep-set spigot bearing in the end of the crankshaft.