I don't know how much detail you need or want me to put on here, so if you could give me a little feedback whether you want this much or not. This is a picture of the old floor pan with the seat belt hole in it. In order to get that hole centered in the new pan I had to start with a quarter inch hole because that's the pilot on my hole saw. I found a socket that's pictured. It's a Craftsman 9/32 12 point socket. A size B drill bit .2380 will fit through the hole in that socket. So I drilled that hole through the socket then went up on top and drilled through that hole with a 1/4 pilot drill bit in my 7/8 inch hole saw.
A socket in the hole ready to be drilled.
It's hard to see here, but the outside hole is centered with the inside hole.
This is a picture of the piece of metal I took out by the farthest back support with the seat floor bracket sitting on top of it.