Michael --- I'm a plectrum banjo player, but I also play a Yamaha flattop 6-string guitar. I made the guitar into a 4-string tenor guitar, with just four strings running down the center of the fretboard and tuned to CGDB, standard plectrum tuning. The neck scale is 24-3/4", and I use the top four strings of a D'addario EJ16 set --- I toss the two bass strings and just use the DGBE strings, retuned to CGBD. Their gauges are 12, 14, 16 and 32, respectively.
This string setup isn't too far from my plectrum banjo setup, which actually uses a GHS #210 tenor banjo set! Those gauges are 9, 12, 22 and 28. Both sets use a wound G string, which is what I learned on and became accustomed to. GHS also sells a #190 plectrum banjo set, with gauges of 11, 14, 17 & 26, but neither the G or the C strings are wound, so I passed on those.
I use standard plectrum fingerings and find that they work just fine on that guitar neck. The shorter scale is definitely easier to play, and I can also make a few chords that my fingers could not reach on the plectrum banjo neck. My only gripe about this setup is that with the somewhat shorter neck and that 4th string tuned down from D to C, getting and keeping that string in tune requires a little extra attention and a delicate touch at the peghead. That could probably be resolved by using a somewhat heavier gauge, say a 34 or 36, if your fingers can handle it. D'addario also sells a EJ17 set, with 13,17, 26 & 35 gauges, which might be worth trying if you need some additional string tension.
I play plectrum banjo and guitar. Played for many years. The banjo is the regular 26 1/4" scale length. Of late I bought a 24" scale length guitar to try with plectrum banjo tuning--CGBD. Tuned the top four strings to plectrum banjo tuning--CGBD--took off the bottom two strings. Result?---Works fine--no problems--good sound.
What I wanted to know is if I managed to find a shorter scale length banjo--say 24" would the sound be more 'shrill' ('trebley') than what I am used to on the standard banjo scale length? There again the banjo tone ring could make a big difference for tone.
Michael -- OK, I understand your question better now, but unfortunately I have no ready answer for you!
My guess would be that it shouldn't sound all that different, because you'll still be using the same CGBD tuning. A true tenor banjo probably sounds more "shrill" because of its higher CGDA tuning. And as you noted, the banjo setup (head type and tension, tone ring, type and height of bridge, the action, etc.) could also make a difference.
You might send an inquiry about this to the OME banjo website -- they sell a 22-fret tenor/plectrum banjo with a 23.375" scale that can use either tenor or plectrum tuning. Here's the link: omebanjos.com/banjos/other/tenor-plectrum/ SETH
I play an Ome shorter scale plectrum banjo that is a custom I had made a couple of years ago. It has 22 frets and can be setup as a plectrum or tenor. Mine is an open back with the sweet grass inlay. It fits my hands better and is fantastic to play!