Is the problem at the rear where the tonneau fastens to the deck or simply getting it attached in the front? With both on my tonneaus issue has always been getting to to attach to the windshield at the sides. Now with Miata Seats and a roll bar getting the tonneau to fasten is a challenge. I'm going to need a little bit of customization done by an upholstery shpo to tonneau fits properly now that I've got to deal with Miata Seats, Windblocker, and a Rollbar. My '69 tonneau fits the seats the best. That was the year of really high headrests and extra large headrest pockets but it won't fit around the rollbar or get close. Got a latter tonneau installed on car in garage right now but might make for curious driving the way it fits currently.
Between my '69 tonneau and the latter tonneau, additional zippers, and some velcro of twist and turn fasteners I can get the upholstery shop to modify something so it fits properly. I saved my old convertible top for additional, "weathered" vinyl that looks period correct to match the existing tonneau. Got a couple of good pics of what others have done with tonneau and roll bar as samples if anyone is interested in creative solutions.