How to frame this wall

Thank you for the advice Re: moisture. The question I have is how to fasten the top of the studs given the location of the duct. The track for my studs on the bottom will be bolted the slab but how can I secure the top of the studs?

The house is in Westchester, NY. The walls are fieldstone with a skim coat of mortar painted with drylock.

They are not level which makes running the 2x2 challenging. I think I will try what you are suggesting building the latter in sections on the floor, then put it up and using shims where necessary to tie it into the concrete.

I am starting by boxing in the ducts with plywood. I was able to use a rotory hammer to screw some pressure treated 2x4s to the field stone foundation. The first piece of plywood is screwed to the joist. The second piece of plywood is fastened with screws at the corner to the first piece of plywood. The other edge of the plywood rests on a level shelf made from pieces of 1x2s.

I will frame walls with galvanized studs. Tracks will be screwed into the slab and the plywood under the ducts. The studs will be 2.5 inches off the wall. Insulation and vapor barrier will be 3 inches of closed cell spray foam.

Any thoughts?

Forgot the link to the beginning of the project. I messed up by putting g dita down first. https://flic.kr/p/GCBDeZ