Rega arms (and its variants) are very commonly used on Townshend tables. My Rock 3 came from the dealer with a modified Rega 300, and I believe even the current Rock 7 is sold with a Rega. So I'm sure the Audiomods arm would be just fine.
Over the years I have tried these arms:
SME V
Graham 1.5 t/c (without the trough as it is a silicone damped uni-pivot)
Kuzma Stogi "s" (again, without trough for same reason)
Kuzma Stogi
Kuzma Stogi Reference
Linn Akito
Linn Ittok IV
Michell Technoarm
All have worked very well on the Rock. I recommend avoiding unipivots as they disallow the huge benefits provided by the front end trough.
The armboard is a simple affair -- basically a 1/4" thick piece of rectangular acrylic, roughly 4 x 5 inches. You can buy the acrylic cheaply online, and easily cut / drill it yourself to accommodate any arm.
