Welcome jdcburg to the forum, glad you joined us.
If you plan to do pedaling then as you pointed out I also believe the friction drive would be a better option. As far as which has a advantage mounted on front or rear? I have only ridden a rear friction drive and I do not see a advantage either way. Maybe those with more friction drive experience will jump in with some advice.
There are several that sell complete kits that you are speaking of, here are just a few.
BICYCLE ENGINE KITS FROM BIKEMOTORPARTS.COM
Motorize your Bicycle with our Bike Engines Kit. Engine Kits include gasoline motors and mounting hardware. Bicycle not included.
Staton-Inc motorized bicycles, bike kits & gear drive kits.
Motorized bicycles, various bike motors, electric bikes or TLE 43 bicycle engines for Dahon folding motorized bikes and tricycles.