SME 20/3 --- tonearm recommendations!?

... the runt of the litter ...

Yes, but still very impressive. Did listen to one last week...amazing Performance.
But that owner did wear a Rolex too :-)
Well, we know, a true Audiophile is born to suffer ... best is to listen to some Arms ...or to learn something about geometry, bearing quality, enery transfer...most Arms work only with a few carts very well, or they give their 'sonic signature' to everything you use .... most don’t care because Hardware rolling is the fun of the game... or a good price beats the ear...I prefer one which is a final statement for every cartridge :-)

I know that it has been stated the the Koetsu will not be a good match to the Kuzma due to compliance. Looking at a cartridge calculator, the Kuzma is 18g effective mass. The Koetsu mass is 9g with a compliance of 5. The calculated resonance is 14hz. If I use heavier fasteners, I can bring the Koetsu mass to 15g and the resonance down to 12hz. Is this a worthwhile approach? I realize if I go this route (Kuzma), I may have to sell the Koetsu..

Its a bit of a fork in the road: koetsu and other low compliance carts go left....medium compliance go right. ;)
Since you have two, somewhat similar, one-arm turntables it seems an opportunity to devote one for low compliance carts and the other medium-high compliance carts is at hand.

mohawk that is absolutely perfect. It is easy to add mass. Much harder to take it away. There are head shell weights you can get that hide under the cartridge. You add weight until you get the resonance down just under 10 Hz. Get The Hi FI news test record. It is easy to use and you can dial things in as well as any tech. Do not trust the math by the way. Use the test record. There are too many variables the math can not predict. The Kuzma is a terrific arm for the Koetsu. It has unbeatable bearings, the vertical bearings are right at the level of the record where they belong and the arm tube is as stiff and resonance free as they get. Also if you were to get a high compliance cartridge you can always tame the situation with the damping system.

Well...this ..."terrific match "...unbeatable bearing" and similar endless praise I did read countless times in the last 20 years even for the worst products/ tonearm cartridge combinations.
None, I mean absolutely none of such "influencers" have the slightest idea about Arm geometry, bearing influence, energy transfer, forces to cantilever based in mediocre design etc. Did own verious Kuzma products and know very well what they can do or not ...one man's ceiling is another man's floor
But each his own :-)