Dimensions on Michell armboard for Rega

I am looking to make my own Michell gyro Se armboard for a rega or OL silver arm (same size) rather than pay the outrageous price of $98 for a round piece of metal with a hole through it that Michell demands. (I would also just like to experiment with the design) If you are a Michell gyro owner could you help me out with the weight and dimensions of the armboard and i would be happy to correspond and ship you demos to try. My first intent is to build one from acrylic with lead shot to adjust the weight(like the Teres platter design). Help an audiophile defeat the shameless price gouging that we are all subject to by sending me the info - Thanks!
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Weight of tonearm + weight of armboard must be equal 1 kilo.
Dimensions are approximately 2" on height and 4.5" on outer radius(you know the inner radius I guess).
I can't help with the outer dimensions, but a 25mm hole needs to be drilled in the armboard, in such a way that the center of the hole is located 223mm from the center of the spindle. The armboard needs to be thick enough to give good rigid support to the arm, maybe 1/2" thick, and allow the clamping of the arm to the board by the big nut that holds the arm to the arm board. The big nut on the Rega should not be tightened more than finger tight, because this will affect the sound quality. Too tight is dead, too loose doesn't hold it in place well enough. Finger tight is good.

If you are making it from acrylic, be careful, because the drill bit can "grab" the plastic at any time during the drilling and shatter it, or yank it off the drill press clamp. Use a slow enough speed to not melt the acrylic while you are drilling the hole. Personally, I'd use hardwood. That is what Teres is moving towards in all their tables and arm boards. You can still load it with lead, and the wood is easier to work with.
Thanks guys for the info. I have a woodworking and small metal shop and machine many types of jigs and small parts out of acrylic, wood and metal - so I figured this would be a piece of cake. I will also try some mahogany and cocobolo I have left over from some furniture jobs. I also plan to make the dust cover (also a $100 retail value) from a few dollars worth of acrylic