I am interested in improved terrestrial radio reception as well. The 89-91 style antenna sounds interesting but I can't seem to find anyone who sells the entire assembly. Most only sell a replacement mast which means sourcing the cable and mount from the junkyard. Also, that style mounts above the firewall and seems exclusive to 81-91 style scuttles and wouldn't work with my 1980 Suburban.
I've had excellent luck with the windshield antenna in all of my 73-80 rigs, and in fact an old 73 Blazer I once owned achieved the best reception I've ever experienced and that was with the bone stock AM-only radio. Upgrading to a JVC AM/FM/Tape in 1982 killed reception and it got even worse when I added a fender mount antenna. I suspect General Motors put some real thought into designing what the did and anything I may try is less efficient.