Rear seat delete panel installation?

[BB67FB]

I purchased a shelby rear seat delete panel for my mustang - the part is for a 65, but I was told it would fit with minor modifications, and after takiing out the back seat and placing it where the rear seat used to be I can tell that it will fit, but now my question is, How? Do you have to drill holes in the panel and mount where the seat was? How were they installed in the originals? Any one have any experience on this?