I've done something similar, but with parts I had on hand. I took a gas-pipe framed Raliegh with Simplex DRs and way-too-high gearing and swapped all the Suntour parts from an old Fuji roadster that was way too small to ride.
Rode that bike for a couple of years till I could afford something better. The Fuji had a 12-28 freewheel that was lots friendlier than the 11-21 on the Raliegh.