Welcome robbomberbomyea! Could you verify if this:
oldroads.com - Vintage Bicycle Picture Database
link is showing what you have.
That site oldroads has Shwinn's listed from 1851 to 1987 and is a good reference.
If so there is a large area for a big engine. I like the DIYer (Do It Yourself) section of this site, but if you are for a kit so be it.
I have my JC Penny Foremost in the same era being completed with a 3hp Briggs engine. For only off road and the pedals are gone now.
For a true bicycle / powered bicycle, both available you must check if you want it legal on the streets and others havde more knowlege on that point. Checking locally with the law enforcement in your area is the best bet first before you end up having no where to ride it.
I am planning to get an OHV (Off Highway Vehicle) state sticker, not a true registration but good for entrance into motorcycle parks run private, state, or federal lands.
Oops, on your info I just noticed you have 3 pics of the Murry Build and in the back there is a chopper bike, besides the motorcycle street bike. You then are into motor bikes quite already!