I need to run an 8″ duct from the attic through the ceiling to connect to a return. It will be in a closet so looks aren’t of prime importance, although I do want a good seal.

It seem like one option would be to run a piece of solid duct through and use some kind of trim ring on the underside that would allow foam/caulk to make a good seal. But I’m having trouble finding such a ring.

Would it work to cut the hole and use an 8″ take-off like this on either side of the drywall?  (I could thread bolts from top to bottom to keep tight.)
https://www.gaf.com/en-us/products/master-flow-air-tite-take-off

Or use two 9″ takeoffs I could slide the 8″ duct through and then seal around the 8″?

Thanks all!