Ralph,
The FR-66 is not a "very high-mass" tone arm- although its on the high side for sure, but not 'very' high.
I think you are mistaken....👀❓
The FR-64s is listed on Vinyl Engine with an Effective Mass of 35Gm..so a figure of 40 Gm for the FR-66s is quite believable...❓😱
I've trawled through the Data Base on Vinyl Engine and can find no arm ever made that comes even close to these figures...😫❗️
Here are the highest masses of tonearms I could find on the Database:-
SME Series V...Mass=10/11
SME 3012R=14
VPI JMW Memorial 9 Signature=9.5
Zeta=16
Technics EPA250=14
Roksan Artemiz/Tabriz=9
Linn Ittok LVII=13.5
Dynavector DV501=25
Here are the Compliance figures for some of the cartridges I have used on the FR-66s:-
Shure V15 Type III Compliance...22.5
Signet TK7SU....30x 10-6cm/Dyne
Acutex LPM 312 III STR....24
Acutex LPM 420 STR...42
Empire 4000D III....30