Assuming you are keeping it friction
Does the current gearing meet your needs?
yes: put a 6 speed free wheel (check with pastorbobinhn) on it, any sram/shimano/Kmc 6/7/8 speed chain if you need or want find a matching front, rear deraillers and nice double crankset (treat the beast to some bling)
no: spread the stays (not hard using sheldon's method... I did 126 to 135 on 82 nishki
https://www.sheldonbrown.com/frame-spacing.html put that ird 12 - 32 on, and put a nice triple up front, with a deore rear derailler of some vintage (new or old)