I can't help answer your question directly....I have no idea which SEM color will match the '88 beechwood dash. When I wanted to repaint parts of my interior (beechwood '88 GT many years ago), I went to an automotive paint store and they custom mixed me a batch and even put it in a spray can. I think I paid $15 or so, but it was well worth it and matched 100%. The bad news is the beechwood interior is comprised of many different colors (dark sienna, light sienna, etc. etc.), so it might get expensive to re-do everything. If you just want to paint the dash one solid color though (like the '88 Formula or coupe), then you should come out OK.
I brought in the part that I wanted painted so they could color match it.....it sounds like you have a gray interior though, so this may not be of much help to you.
Good luck.
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