Updated below in Bold Face.

This is a shot of the right side mount of the original fiberglass seat which is still commonly seen in SRFs. The metal strap under the three bolt heads is a critical piece of the mount; it was added after failures occurred in crashes. It is sometimes left out during assembly; not all SRF owners understand its purpose.
This spring I saw a couple of SRFs with damage to the fiberglass at the rear end of the valley on driver's right between the seat and the mount; this is something that an SRF owner with one of these seats needs to keep an eye on.

This is a shot of the top of the seat back, where the shoulder harnesses exit the bodywork. This car has the original shoulder harness mount points, which are 8" center to center. The GCR specifies that this dimension should be 4"-6". A kit is available from SCCA Enterprises that allows for more appropriate (and more GCR compliant) mounting. I understand from Shawn Morrison of Motion Dynamics (the NEDiv CSR) that it's a bit of work to install properly; it can be bolted in but is apparently best if welded.
One important point about this type of seat -- we impounded SRFs at the NARRCOffs on Friday afternoon, and two of the cars we inspected had noticeable fraying problems with shoulder harness webbing where the harness came in contact with the rough edge of the fiberglass. It's something an SRF owner needs to keep an eye on.

This is one of the newer style Butler seats. Drivers who have switched definitely like these better. One key point here, though, is that with unmodified shoulder harness mount points, the belts are pulled inwards and the harness tends to bunch up where it passes through the seat. We would very much prefer to see harnesses laying relatively flat where they pass through the seat. In fact, the 2007 GCR 9.3.18.D (page 78) says this:

The seat itself, or anything added only to the seat shall not be considered a suitable guide. Guides must be a part of the roll cage or a part of the car structure.

Here is a Butler seat in a car with the new style shoulder harness mount. Note how the belts now lie flat and run straight from their mount over the shoulders. This is really what's best all around.