My sincere thanks to everyone for all of the excellent input! It proved very useful and enabled some more interesting reflections as I went through the evaluation process.
Which turned out to be far longer than anticipated. Did the geometry check and everything was fine. VTF was fine as was overhang, alignment & azimuth (elliottbnewcombjr
the headshell is integral, so that was an easy check). Then came the speed check. Sloooooow. Needed an oil change - very sticky. New oil and an hour of spinning by hand to seat the assembly. Looking good, replace belt, platter on, strobe disc on, power on. Still slow.
Scratching heads. Poke at the motor suspension, make sure it's got reasonable torque, watch the action on start. Nothing unusual. Two other belts making sure they're properly seated due to the rectangular cross-section (hint), re-level the table, same result.
Put a drop of lube on the top motor bushing, let the whole thing spin for another 15 minutes. Still slow, motor presumed going south. Very bummed as this table is a nearly perfect Planar 3, maybe 1985 or so. Not a blemish anywhere and the dust cover has nary a scratch. The arm is pristine and if it hasn't been recently restored, it was kept in a nitrogen filled box. Zero oxidation anywhere, tight bearings, no scuffs, nothing.
I tell the tech I just can't spring for second table that will immediately eat a $225 motor kit, he says talk to the boss man. Tell him the deal, he's not willing to move that far, so looking dim. Suddenly the tech says "check this out." It's running spot-on 33.3! Turns out the wrong belt had been installed. My last rebuild on a Rega was back in 1983 and had forgotten the belts are O-rings. The tech had found a genuine Rega belt and tried it. That little bit of difference in circumference from rectangle to round... Note to self and those of us in a certain age bracket - don't trust your recall!
Play a part of a track, definitely stereo, in-phase, stylus not damaged or mis-tracking. Take a closer look at it with the bench mag. Not an ADC, it's an Audio Technica AT440ML. Another note to self and others: Use a magnifying glass when looking at small print.
Which turned out to be a good thing because the 540ML can't readily be had at the moment - supply chain SNAFU. Not expected until Q1 2022. A new stylus is still needed, but I can take my time on evaluation. The Nagaoka tksteingraber
and jerryg123 suggest is an interesting alternative as is Grado idea from @yogiboy
Fortunately, I have time to consider this in more depth because I spent a lot of time I didn't intend on due diligence. There's a lesson there!
Thanks again everyone!