Thanks for the replies.

As pointed out by various posters, I was probably making it harder than it needed to be. The slot is 14mm X 5mm, allowing a little play, so as not to be tight as a gnat's chuff. Wickes sell steel bar in precisely that profile, so a simple solution. I can fix some studs into the bar to give fixtures for the jig at table level. Job done.

Cheers.

Bill.