I had the 65 panel in my 68. What you will find is that the recess for the tire is limiting to about a 195 profile tire.
There is a spot in the molding of the panel that indicates the location of where you must cut through the panel fpr the spare "hook mounting". That is going to be what you use as a pattern to mark the location of the mounting bracket.
If you are open to suggestions, I'd recommend that you go with the 66 version of the panel in fiberglass and eliminate the spare tire from the interior mounting.
The fiberglass version needs no additional supports. The origianl "plastic" one did. It would turn into silly putty in the sun.
The original mounting method of the spare, although acceptable for the time, is at least questionable.
The compressability of the tire itself makes it next to impossible for you to mount the tire firmly and it really is only semi-fastened in place.
IN ADDITION, if you plan on tracking the car at all, you are likely to find that the tech inspectors are going to REQUIRE you to REMOVE it from the car to run on the track.
SOME may permit it to remain IF it is firmly bolted down, like it would be mounted to a wheel hub, with FIVE bolts, BUT I WOULDN'T count on that ruling.
It is simply much simpler and less liable for them to make you remove it from the car to run. MOST make you remove any spare from the car even in an enclosed location like the trunk.
It's also entirely possible that since your car ISN'T an original Shelby, your local state inspectors will not pass the car with the tire in the 65 Shelby location.