Just look at my 73 and see screws from the door catch are slightly in the way. I piece of 3/4" rigid conduit fit all the way to the bottom of the tub without a problem. I measure the lower plate iny 73 around 7". Easy to measure hard top sides including the 72 hard top that was on it when I bought it at 8". Your hard top possibly been bend to make it if. I take the approach to fix what preventing a piece from fitting verses modifying the piece that doesn't fix.
I am curious what do you do for the piece on the B pillar that fills the section for the doors? Does the B pillar have the bend to match the door? Also the bow in the rear would have gone between the bolts. Your using the forward bolts. Factory FST used a bracket held with four bolts originally that centered the bow. Around 71 switched to a two bolt style that may have worked with aftermarket bows. Here is a picture off the bracket on my 73.
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At the top of the tub is uses a two hole strap to hold it tight. Other pictures shows the fixed nuts.
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Easiest picture I could find of a B pillar bow. Back has a channel the top slides down to hold it in place.
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