The flat non-A/C as well as the flat version with the convenience control option both have tabs that align with holes in the metal dash, but I agree that the larger panels on each side have posts and the plastic center piece is clamped in place. No dedicated fasteners.
However, for the A/C version, which is much heavier - metal vs. plastic - there are threaded studs. The Ford electrical assembly manual (published by Osborn) shows a quantity of two 371024-S2 nuts for the A/C option only - no fasteners without A/C.
According to the Ford standard and utility parts catalog (1969 version) a 1/4" "nut - self threading" type 1 is listed as 371024-S7, which has a different finish. Attached is a picture from that catalog.
The Obsorn/Ford diagrams are copyrighted, so I'll respect that and won't post pictures from it.. You should consider picking up a set.