Finding a Harley swing arm frame pre-69 means your motor VIN still works. That would be my choice. Shorter fork tubes will get you close to stock appearance with a 16" front rim.
Have fun, you have the makings of a good classic Harley.
Go to a swap meet and get a used OEM Softail frame. The Shovel head should fit. Ask for a BOS and title if possible. Save any receipts. I'm not 100 percent positive but the trans may fit as well. If not, buy a 5-speed transmission with an MSO. That will lower your engine speed at 60 mph.