This excerpt from McFarlane website has reference info for fastener numbers, drilling new seat rails and substituting screws for rivets if necessary:

FAA General Aviation Airworthiness Information Bulletin CE-90-03R2, 08/26/2002 Original Issue 01/16/1991

This alert gives direction for the replacement of seat rails for most Cessna airplanes as required by AD 87-20-03R2.

It advises all owners and operators of the necessity to install all required fasteners when seat rails are being replaced.

Many seat rails are manufactured with pilot holes only and do not contain all holes required for installation of the seat rail in the airplane. It is, therefore, necessary for the installer to assure that there are sufficient holes to accommodate all required fasteners.

Note these recommendations:

When replacing a seat rail, note the number and location of all fastener holes on the seat rail being removed.
Match these holes against the holes in the replacement seat rail. If the replacement seat rail does not have all of the same holes at the same locations, they must be drilled.
Since it is difficult to install many of the rivets required to attach the seat rail, it is permissible to substitute screws with ultimate tensile strength exceeding 50 ksi.
Example of such screws are AN515, AN520, AN525, MS35206, MS35207, MS35214, MS35215, MS35218, MS35219, MS51957 or MS51958 with lock nuts, provided the holes are ream fit and spotfaced.

For further information contact your local FAA office