I will look into the other TRANSIT forum. The reason for my question I am wanting the room of the Sprinter 170XL. The Transit 148XL has about the same cargo area of the Sprinter 170, but has a higher head room and less drawn in sides at the roof line for a RV build out. Transit does make a 172 wheel base for class C RV build outs.Go ask on the Transit forum. There is a guy there who is well connected. He works for Matt Ford.
He will probably tell you no.
there are advantages to a 148 wheelbase on an extended. Better turning radius. You can back the end over a curb and grass and fit in a regular parking spot. Break over is improved at the expense of hanging up the rear on a steep transition. You can always airbag it to help this.
Looks bad with that big back end but the Transit loses to the Sprinter in every looks department in my opinion.