Alright, i think i know what i want now.
Used Regan 250
New Denon-DL 160
MICHELL TecnoDec ARM BOARD for Rega Tonearms - Great DIY boar
If this won’t, please let me know.
Used Rega 250 is fine, I don't know if a DL-160 would suit, but it may well do..
Michell Technoweight may well a good upgrade (I have one waiting to go on my Tarantella / RB300)
But if by armboard you are referring to the horizontal square the arm is attached to, then I am not aware of any Michell offering which will fit.
What you need is a 4" (102mm) square of something rigid, with 6mm (1/4") mounting bolt holes drilled on the corners of an 80mm square in that board. I will attach a template I posted earlier for the positioning of the 25-29mm (1"+) hole for the arm pillar.
This board needs to be no more than 12mm (0.5") thick, and needs to to be lifted from the subchassis so that the top of the armboard is about 31mm (1.25") above it, using rigid spacers.
Popular materials for the board are black acrylic (e.g. Perspex) or a 0.5" carbon fibre/end-grain balsa sandwich.
The Funk Firm used to make them, they may still do so, but they are not listed on the website. I make them, and postage may not be too expensive from the UK to the US. Equally, you may be able to to it your self, or know someone who can.