I assume you were paid out by your insurance company?
If that was the case then your issue is with your insurers who would have become the legitimate owner once they paid you out, and it s not unusual for a stolen recovered vehicle to be sold on.
Have you been trying to find out for the past 30+ years?
I take it that it had particular identifying marks for you to be able to recognise it despite being on a Q plate? Usually a stolen recovered retains its original mark and is usually only issued with a Q plate when its identity or year of original registration is in doubt.
But 36 years on, the chances of you getting a response now is zilch, and once you ceased to be the legal owner they are not obliged to tell you anyway, all you can do is write to the insurers again, but I bet they have nothing on file after all this time and the Police certainly will not have retained any of the paperwork for a straight stolen vehicle even if somebody was prosecuted.