Tonearms - SME 3012, Jelco, or Schick?

what other long arms have removable headshells and easy height adjustment?

Thanks for all the information!  Very helpful indeed.  I will look at all the recommendations.

Cartirdges - It will be a moving coil, most likely a Umami Blue or ML, possibly a Dyanvector DV-20X2L or a DRT-XV-1s.  No SPU's although having one intrigues me.   My TT can support 4 arms, what is on there now is a Micro Seiki CF-1 with a AT VM760SLC and a Grado Arm with a Sonata 2 cartridge.  So all of this is a setup in performance.  I'd rather put the money into a cartridge than in the Tonearm, although I suppose I can buy a lesser cartridge and a better tonearm.

BTW, I only have a few mono records.  These are from Mom's estate, so mostly big band, 1930's to 1950's jazz.  Some are in very good shape, some are not.  I thought about a mono cartridge but for the few albums I have, it doesn't make much sense to invest that money into a mono cart.

I have an SME that I liked with a Benz Glider, but prefer the Jelco 850L if you find one, especially with the adjustable VTA for it. Using it with a Benz Ruby H, and have been happy for several year..

If you can be lucky enough to find a Jelco TK-850L, jump on it.  It was the last generation Jelco and is quite good.  Earlier Jelcos are lesser performers, but the better ones are OK.