I’m going off from the original question but as the topic is “Series V rear bench trim question.”
I’ll continue on my Series V
.
The studs shown in Aladin picture as said hold the carpet down there are 7 Total of this style with the longer spacer.
4 along the vertical wall 2 behind each seat, and an additional 3 across the back of the parcel shelf one in each corner and 1 in the centre of the raised tunnel. These are the long prong ring snaps sold by Sunbeam Specialties part #UK58C They don’t sell the longer spacer
The 4 Studs along the vertical wall as pictured also hold the original rubber mats up in place. The mat has 4 round cut-outs to go over these and then the carpet snaps in place.
The Snaps as pictured above without the longer spacer, are also used in the front foot wells 2 on the driver side 3 on the passenger side to hold the original mats in place. The Series V didn’t have full carpeting, I think the GT did.
I don’t know what is being sold now as an interior carpet replacement or how it attaches.
To the current question you may want access to these longer snaps if you carpet up the back vertical wall. Not knowing how that and the parcel shelf carpet in the new kits are finished at those 2 edges.