The door frame inside top pieces on a CMC are indeed rounded. The ends where the furrels for the side curtains fit are filled in (by the builder - you) with epoxy fiberglass filler. The aluminum furrels then are inserted in filled area. If yours aren't solid there now - they could be taken apart and easily filled. DrClock has a local machinest make the furrel and offered a batch up for sale awhile back. Very high quality compared to the OEM Home Depot looking ones. Do you have the CMC chromed brackets? They cn be replicated with SS bolts - do a search here.
The drawing in the manual makes it look like the pieces sit flat on top of the door -- they really mount flat to the inside - but there is room to drill for the furrels.
