[Tishabet]

I've had a 73 and 74 and have removed the seats in both, but I know there was a change in the manner of seat attachment somewhere around 70 (having bought pans for meant for a 60's car and having to retrofit the hardware to fit my 73) so this info may or may not be helpful... in the 73 and 74 there are rails on both sides of the pan (one against the center tube, one against the heater channel/door sill) and a sort of hump in the center of the pan where there is a captured pin (attached to the spring and lever combo you reference) which allows you to adjust/lock the seat.
First things first: If you're seats are like mine in the 73 and 74, there are plastic caps that go on the ends of the rails on each side of the seat which need to be removed before the seat can be removed. Also, sometimes there is scale rust or a coin which gets captured in these rails and causes the seat to bind when moving forward or backward.
The procedure as I recall it is to remove the plastic caps, vacuum out the rails to remove any particles of rust etc, have someone hold the adjustment lever back and slide the entire seat forward until it is off all three rails (the left, right and center rails).
I know there are plenty of VW fans on this board... don't pull out the F150 yet!