Before attempting to modify a non standard part to fit, remove the seats
and take a good look at the original rails.
Make sure the rails that bolt to the seat frame are straight. Many time
over the years, the seat frame has sagged a bit and put a slight bend in the
rail. If it isn't too bad, shims under the appropiate mounting bolt(s) can be
used to straighten the rail.
Also check the floor rails for straitness and for any twist they may have
Replace the floor rails in the car, minus the seat and check that they are
parallel. Again, shim where neccessary.
The wooden spacers may have deteriated over time and are allowing the rails
not to fit properly. Replacement is the best answer.
Finally, grease the rails and the latching mechanism with a good white
lithium grease and make sure they slide easily on the seat frame before
re-installing the seat.
When replacing the seat, insert ALL bolts and start them, then gently
wiggle the seat assy. to get everything settled. Before final tighting, check
the seat for proper operation.
Actually it probably takes longer to talk about it than it does to actually
do it. A good Saturday afternoon project.
Sorry about the length of the reply, but I've come down lately with a
severe case of "Flap-Jaw"