Put one in my '70 Mach 1 about 3 years ago. TMI was the supplier.
Great fit, more headroom, no worries about a drooping OEM style headliner. Only has to remove one rear quarter window (pass. side in my case) and with the windows down, the one piece headliner slipped right in. Added a insulator on top too before finishing the install. Btw, the sail panels fit better too as the very stiff headliner won't allow the top/front edges of the sails to flex and, sometimes, slip out/down a tad.
Other than the cost, I'd highly recommend this welcome and modern addition to a now 50+ year old car design.