would a shelter 501 work well in a michell tecnoarm?

i used to have technoarm/shelter501 combination.
never found it harsh or bright. contrary it was very well balanced and smooth.
you might want to adjust VTA.

How old is Shelter?
Didn't mention hours too many or too little...
My Shelter is definitely due for re-tip and harsh in inner grooves in almost all of my records with small exceptions on high-quality deep grove cuts.

I had Gyro SE no chassis vs. Gyrodeck. Perhaps no chassis Gyro SE may sound better. Mine was standing on acrylic 2" thick platform. 
For the turntable periodical maintenance, check spindle bearing lubrication, refit/clean the suspension springs. My antiskate was always set to 0. 
Also by slightly changing the angle +-1deg of tonearm you can change effective length, but another tangential cartridge adjustment may be needed. 
I also had improved the way to mount the armboard with teflon washers. I found the original provided ones too stiff.