Michael,
That Ace Bristol, BE 1058, is listed in the A.C.O.C. Ace Bristol Register and shews as taxed in the DVLA car check pages. The location is in the home counties. You could write to the A.C.O.C., attention of the Membership Secretary, asking that your request might be forwarded to the owner who is listed as a Club Member.
I hope you will be able to take your partner's Dad to visit his old machine, relive a few memories and take a few photographs.
Good luck
Barrie