Did the 3/4" work? TIA
@Onward4x4 , The 3/4" plugs were a little large as is and kept popping out as soon as I put them in, so I sliced off the "fins" on all four sides, added a little strip of double sided tape to two edges and then installed them. They've been in for over a month now and I've run both the a/c and heat at a 5 on the fan speed with no movement whatsoever.
Right now I've got every other space filled in, but I may go back and fill in some of the open spots depending on how well the air is diffused across the windshield in defrost mode. I haven't had a chance to evaluate the defrost yet as temps haven't been that cold here.
FYI, the tops of the 3/4" plugs are a little too large to fit into the open spaces, so some trimming or sanding of the edges will probably be required.