drisee

I've been looking around the forums trying to answer this question without starting a new thread but i can't seem to find the answer. If anyone has an older thread you can point me at please let me know but the ones i've found don't quite answer the question.

My '87 Pinarello Montello has a Campagnolo Super Record group set with friction shifting. The prior owner had already replaced the original freewheel with a 7-speed, 13-26. I'm trying to access a lower gear for the hills where i'm having a hard time keeping up with other guys i ride with that are on newer bikes. I love vintage bikes so i won't be getting a new bike but would love to keep up better.

I don't want to mess with the original cranks or the FD or RD. I believe my only option without replacing some of those other parts would be to replace the freewheel with a 13-28, which my RD should handle fine. I'm wondering if I could go even lower then that to perhaps a 13-30 7-speed that would still work with my original RD?

Also, what is the best freewheel brand i could buy? SunTour, Shimano, etc?

Thanks so much for the help.