Okay, here are some pics. There are possibly fewer snaps involved than you might imagine.
On the drivers side I found two,, at the rear edge of the footwell floorboard:
The other end of that carpet is secured by a pair of clips. If you haven't worked with these yet - be advised they bite. I have bled more than once when attaching the carpet and not paying close attention to what I was doing.
The passenger side is like the drivers side, but here are some photos to confirm:
The carpet under the seat is held in place by virtue of the seat rails being bolted through it. The floor piece behind the seat just lies there, didn't see any snaps.
Here's a bonus pic I took while crawling around. A velcro'ed pad made for cushioning a seat belt (so it doesn't chafe your neck) can be strapped around the console support to add a bit of padding. That piece is hard metal on a TR4, possibly later versions were somewhat padded.