Stem shifters are on the stem.
Downtube shifters are on the downtube.

Antieverything is right that it shouldn't make a big difference with friction shifters. Most of them should have adequate throw for using with most front derailleurs.

I am right at the maximum range for my old Campy shifters + an Ultegra rear derailleur + 9s cassette. So, the rear derailleur pull may be an issue.

I also have had problems with clamp-on shifters and OS tubing. I did manage to force a Suntour stem shifter onto an oversized stem, but it was a tight fit.