Looks like it came with period BioPace egg-shaped chainrings. I like them, although some people don't.
Took a similar bike from a 6 to a 7 speed freewheel, first with a 7s downtube shift lever, and later with a pair of Sora STI brifters. A short cage Shimano 105 rear with a 42/52 BioPace front handles a 13-15-17-19-21-24-32 cluster ok. A 13-30 rear has about the same range when used with a 39t front. If you have been avoiding hills, the 30 or 32 tooth bailout cog makes a fearless go anywhere setup while keeping the original double crank.