I’d never seen nor heard of Kent Cigarettes before, though that probably has more to do with being a non-smoker than anything else.
The only ‘nice’ paper stock in the entire magazine is a double-sided full color heavystock gloss (I’m not going to try to guess the weight) advert for Kent Golden Light and Kent Golden Light Menthol Cigarettes touting them as having the lowest tar of all leading brands.
By 1977, Kent cigarettes had gone for two decades without using blue asbestos in their filters and were also being used as currency in Romania.
I’m pretty sure all 3 issues I have feature Kent cigarettes as their primary non-publisher sponsor. I’m not saying that Kent was bankrolling the entire Magazine of Fantasy and Science-Fiction operation, but given that their ads are on nicer paper than the cover binding, it makes me wonder!
Other ads in the June 77 issue include an offer for framable quality posters of past covers, a few various offers direct from Mercury Press (the magazine’s publisher), including a T-shirt ad, and a membership offer on the back cover from the Science Fiction Book Club.