Look at where the bottom bracket and the rear axle dropouts are. When the frame dips below that level it reduces the ground clearance. You need that ground clearance a bit more on a stretched frame than with a normal wheelbase.
There can also be differences at the rear dropout area that could affect how well a rear hub motor and/or torque arm will fit.
[EDIT] Some of the Basman frames aren't as much stretched as they are feet-forward. Is a long wheelbase stretched what you are wanting?
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