If the Sugino crank is an RD2, it has a 130mm BCD, go with a 42t. Once upon a time that was typically the small ring on a road double. Ridden many miles with a 52/42. You can go as small as a 38t, 39t might be more common, if the 42t is still too big of a chainring.

John

Edit added: This is probably the least expensive route. If you change cassettes to one with a wider range (larger cog) you "may" have to change the rear derailleur; i.e. 28t to 34t.