The RB303 arrived today and I was able to install it before the surgery. Here are some installation notes.
As to Watercourse's concerns above:
As best I could see, the two mounting holes closest to the cartridge are set at 90 degrees to the axis of the arm's hardware: the bridge which runs out to the armrest.
So I slid an artist's triangle in to engage the side of the turntable and those two holes, and clamped it in place:
Marking for drilling was not too difficult: I used a mechanical pencil, which just made it through the mount to the plinth. (Rotate the tonearm for access to all three mounting holes.) Once I had gently tapped in starting points with a punch (to counteract 'walking' across the laminate), I used a 5/32" bit.
I used 2" 6-32 screws (tops sanded, primed and sprayed satin black), flat washers and thumbscrews. They match 50mm in length, but could have been half an inch shorter.
Interestingly, the phono cable is so large on this arm that it's very hard to get flat as it exits the tonarm- flat enough not to become a fourth foot. The supplied mounting clamp has to be located close to the center of the rear of the plinth so the cable clears the new mounting screws.
The antiskate isn't mentioned much in the instructions. It's a round knob unlike the 300's sliding control, but the mechanism must be similar. What looks like a knob is really a plunger you move in and out to adjust antiskate. This took me a little while to figure out.
I am currently running an SAE 1000e cartridge. The cartridge mounting slots on the RB303 are just
a bit too short to let me extend the SAE out enough to properly line up on my MFSL Geo-Disc. The stylus tip sits on the edge
of the hole it's supposed to be sitting in. Tough nooooogies...
My GrooveTracer counterweight simply slid onto the Rega Planar 3's RB300 end stub. Frank tells me I will have to install the GrooveTracer stub to use his weight on my new arm; it doesn't fit as of now. I'm going to tackle that later on, probably tomorrow.
That's what I've got for now.
Rega RP3, TTPSU, Groovetracer delrin, reference subplatter & counterweight, Lim double pulley
Shelter 501-II with Soundsmith Level II, Heed Quasar