Thanks for the feedback.
There is about .080" clearance between the aluminum plate and the brass element. I was thinking that it might furthest help prevent the heat migrating up the tube. I guess the plastic doesn't conduct much heat anyway.
If I support only at the top, I'll need to connect into the groove somehow.
On adjustment, I was going to make one of the corner holes in the carriage close and the other three a bit oversize. This would allow you to rotate the assembly to get the nozzles at the same height. I was thinking you wouldn't do this real often. Is this a bad assumption?
Would you put the fan on it and if so, do I need to shield the airflow from the brass head?
I'm pretty slow at CAD. I really hate to make any improvements if it means re-drawing. :