would a shelter 501 work well in a michell tecnoarm?

I'm not sure how much better the Techno Arm is vs. OL 250.  I would find it hard to believe that it would change things as much as you'd want. I don't think the Michell arm eff. mass will be that much better than the OL 250.  Did you buy the 501 from a dealer?  I would rec. talking to Jay at Audio Revelation. He sells Shelters and OL arms.  He's a great person to deal with.

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.

not too old: 4-500 hrs.Sounded very smooth on a LP12/Ittock before I moved it to the gyrodec/rega

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.

thanks for the responses
I tried adjusting the VTA -lowering the arm- but it had a helpful  but limited effect
I also added some weight to the headshell-again a limited effect.
Tortilladc: did you find that adding the weight made much difference to the tonal quality??

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.

I recently purchased a 501 Mk III for use on a Rega RB303 arm. Based on the results of this calculator, I added a 3 gram weight to the headshell. I have no idea if your problem would be fixed by that but it’s a cheap fix to try.
http://www.vinylengine.com/cartridge_resonance_evaluator.php

edit: i also had it professionally setup so there's that too.