What are differences between 67 -72 bench seats ?

[Green Machine]

I need to order new upholstery for my 68 C10. i have heard there is foam and spring differences and that makes a difference on what will fit. I would like to use a hounds tooth pattern from newer model but not sure it will fit. I also have a 1970 and I looked at the seat it in and cannot tell any difference between the two. Any help identifying it or what to look for would be great. Upholstery is generally not returnable, so I want to get something that fits.

I have also heard there is a difference in the seat tracks, could someone explain this also ? Thanks.