G' Day Mark,
I have done it the same way you talking about.I have used two 8mm plate one welded to the pier drilled and taped the other just drill and taped I have used thread bar. The thread bar is flush with the top with a nut under the top,plate to secure once you have it level and if you have a bigger gap between the two plates you can store thing their like eyepieces .I can take a pic of it if you want .
Ian C
