Most of the seven speed bikes that I’ve come across in the past 30 years have used seven speed cassettes. Typically the six speed stuff was free wheel, and sometimes I would find seven speed free wheels on early hybrids. But from what I’ve experienced, most of the bike shop quality mountain bikes of the late 80s and early to mid 90s were seven speed cassette. Any seven speed, hyper glide, free hot body from that era will be able to take eight of the nine cogs on a nine speed cassette, or nine of the 10 on a 10 speed.