I would check the assembly manual.
Unfortunately, there is no "1969 Mustang Interior Assembly Manual", but there is a 1970 version. Going on the basic premise that the 1969 and 1970 Mustang models were "similar", the 1970 Interior Manual (AM0032) shows no screws used except at the sill plates. I refer to pages 48, 49 and 50 (pg 50 for sill plates, the console is on page 51).
The interesting part is that floor mats are shown without "optional".
Jim