Jim, you can do it checkout dmb's Stretch Cruiser with KTM50 / Morini S5.
Franco Morini S5 Engine 50cc
This engine is the most popular, from the late 1960's, up until 2001, and used by many various motorcycle manufacturers, it is unusual because the kick-start lever goes forward (opposite to a normal bike). The S5 has a vertical cylinder with the carburetor bolted on to it.
Manufacturers that have used this engine are as follows:
Italjet/Indian, Malaguti, LEM, KTM, Husky, DBM, Young Rider plus many others.
In the early 1990's the engine was also developed for more power, this included 2 and 4 reed valve cylinders with big cooling fins and bigger carbs (S5GS).
Manufacturers that have used this engine include:Husky, KTM (pre 2001)
The Husky version of this engine was fitted with an ‘O' ring head gasket & thicker base gasket in later years.
Hope this helps Jim!
I can't remember who but one of our fellow forum members did mount a ktm 50 engine into their Stretch Cruiser. I just remembered it's none other than Custom Builder DMB!!!
Oh yeah it is dmb's Stretch Cruiser Builder, here's the Link to DMB's Stretch Cruiser Build with KTM50 engine!