These days it seems TMI is the largest supplier of boots to vendors. Last year I rode the merry-go-round with them regarding a new boot for my 73 (a tear and the snaps kept breaking) but I will be remiss if I don't mention they were extremely responsive to the issue and handled the problem promptly and with courtesy. We went thru three replacements in as many months because the snaps kept breaking or popping thru the nylon retainer strip. The actual fit was, if anything, a bit loose in the final product. The first one was too tight and tore in the passenger side front inside corner - even after I let it lay in the hot sun for 45 minutes. The next couple were cut a bit looser, so that issue was resolved.
My experience is the boot is always a bit tight in the beginning of the season after the car has been tucked away for 5 months of winter. Once it spends some time in the sun, it conforms (stretches) just fine. Obviously, the boot should never be a struggle to install resulting in being drenched in sweat or ripped fabric. It usually takes me about 3 minutes to install the boot (with foam pads) once the top is down.
There is an outfit called Convertible Top Guys who advertise that they make them to order. Their price is about $50 more than TMI. I do not have experience with their product, possibly someone in the forum can chime in. They are located in Rhode Island.
Bill, you bought the boot from me and the company that sent you multiple replacement boots was Distinctive industries not TMI.
We had the same issue and fixed it by making the factory dents deeper in the tops of the inner wheel houses.
Ford beat the top of the wheel houses down to make room for the top frame. We
took a big hammer and made them about 1/2 inch deeper. This lets the top frame sit lower and makes more room for the boot.
We can drop the top, snap on the boot, and then bump the top switch just a bit to take out the slack.
Paul of MO
Paul, that's probably the best fitting advise.
There were fit issues when the cars were new, now with tops being replaced, different materials, out of adjustment or having 40 year old tops on them. It makes it hard to make a boot that fits all the cars due to the variables.