Get the bloody thing to HiFi dave - he's not really that far from you in Norfolk. Why? because he (and I independantly) have set up hundreds of Rega decks with RB300's and he'll know in seconds if you're over-worrying about it.
My own experiences for what they're worth, have been that firstly, the RB300 series use a TAPERED arm pipe, which magnifies any supposed VTA issues. the other thing I found, which some here have disagreed with me on, so take your pick, is that the RB300 on a Planar 3 sounds best firmly bolted to the plinth (Rega may be able to supply you with the original nut which had an infill for just your issues, the infill taking up the slack in the hole and threading deeper up the arm pillar (I think it was first used on the R200).
Many of the Planar 3's I sold were with tallish cartridges (the K9 was "the thing" back then, before we switched to the 1042 Goldring). The sound was better with the arm left as-is with no spacers.
Good luck, and give friend Dave a ring to confirm what I've said.
P.S. below a pic of the R200 nut you ideally need?
Last edited by DSJR; 03-05-2012 at 11:37.
I can't go on and I can't go back, I don't feel so matter of fact,
I tried and tried to make good sense, What's the good to try it all again?