I made this very simple little height tool in 70's for one of those universal dovetailing jigs.I think I saw it illistrated in a B & D router book but not sure: maybe very early Fine Woodworking. Once you have tweaked the correct depth then adjust the bolt through the U until it just touches the bit and tighten the nut below & above the U section so that it is locked in place.
It would be better with a brass bolt but I never damaged a carbide dovetail bit with it. Originally I was going to cut off a short piece from a U channel aluminium "straightedge" but thought I didn't want to loose that 2". I therefore simply formed the flat zinc sheet to suit.
If working with multiple jigs then a wooden one with different heights cut with a straight router bit or dado blade may be the go.
It is very simple & does the job.