The instructions that are supplied with the Standard TM27 show it is a single port design.
https://www.rockauto.com/en/moreinfo.php?pk=45220&cc=1132995&pt=8500&jsn=2067
The '73 FMX w/351 would use the Black band modulator - TM-18 or D3AZ-7A377-A. There's a couple on eBay. You can also use Standard Motor Products TM-27. The current version is a single area diaphragm, the original was a dual area diaphragm (two ports)...
Been doing some spring yard cleanup and removing stumps. My neighbor has some toys and offered to come do the hard work. The space next to the garage will be filled and levelled for a gravel parking area.
When I pulled the interior out of the Cougar, a couple screws and the knockout for the accessory power feed were stuck to the underside of sound deadener. In the Mach I found a handful of trim screws and a quarter window trim.
Exactly as Chuck said, that's how it should have been handled. It was quite obvious the seat was never installed. That's the difference between sales and engineering.
Somthing that applies now more than ever - "expect what you inspect"