You are correct, sir, first off there are no specific kits for formal weatherstripping, however, the company mentioned above, does sell a weatherstripping by the foot That will work for your car, I think it mimics a GM style. I measured my 77 and it came out to around 14 feet of stripping, just an FYI, you will need to save all of your corners, as they don’t make them anymore, and most I’ve experienced are in good shape. It’s just the long straight pieces that get dry rotted, so about an inch past each of your corners, cut and save. You can then glue the weatherstripping to those corners, hope that made sense. Lol.
Also, as mentioned, when you call this company, there is no part number. They have it labeled as “75 roof rail”.