90%o of mono cartridges currently sold as NEW, are in fact stereo cartridges adjusted or modified to produce a mono signal. One of 2 methods is used: 1) standard internal construction, with coils in an "X" pattern, with L/R internally combined to create a mono signal. 2) modified internal construction with coils in a "+" pattern to minimize impact of vertical modulation, and then internally wired to produce a mono signal. Note that in both cases, the cartridge responds to vertical signal. The fact that vertical signal is present and then suppressed, canceled etc does not remove the content. Presence of vertical signal introduces phase anomalies that are audible to some people (not all). OTOH, a true mono cartridge has a single coil / one coil to respond to horizontal movement ONLY. It may or may not have vertical compliance (many don't, some do), but signal only comes from horizontal movement. There are very few true mono cartridges available. Denon 102, Ortofon CG25DI MKIII, and a few other high end Japanese designs (Miyajima, Koetsu ?).
Stylus size and profile are functions of what you will play.
Mono microgroove LPs, pressed from 1947 until about 1958-60 have a " U " shaped groove, best traced by a conical stylus, and are best played with a 1mil stylus profile. Mono LPs pressed from about 1960- the end of vinyl production in about 1969 have a " V " shaped groove, and are best played with a 0.7 mil stylus profile. MODERN MONO REISSUES (to the question of the original post) are pressed with a modern " V " STEREO groove, but a mono signal (IE equal in both vertical and horizontal movement), and are best played with a MODERN stylus profile.
There is some merit to playing a pre 1960 pressing with a smaller, more modern stylus profile. A typical TT of the pre 1960 era was a blunt instrument, tracking at 10g or more...even the popular GE VR series needed at least 5-6g to track effectively. High stylus pressure, crude arm geometry, indifferent handing led to excessive wear at the point where a 1mil conical groove made contact. A modern 0.7 mil or smaller stylus may contact a portion of the groove exhibiting less wear and sound better overall.
Since the original question concerned playback of modern reissues of "Long Hair" music, I would probably lean towards a modern "mono" cartridge with a modern stylus profile. Should the author acquire some/more original mono pressings, then purchasing a true mono cartridge may be justified.
Disclaimer: I went down this rabbit hole and now use a separate TT (Technics SP-15 and AT 1503 MKIII arm) with an Ortofon CG25DI MKIII mono cartridge, tracking at 3g and using a 1mil conical stylus. Sounds GREAT; both better and different than a stereo cartridge playing a mono LP. Not for everyone, but works for me.
