You can add me to the legion of folks who did the Bonny seat mod. I installed the wiring for Larry Law's 12-ways and then I installed the 6-ways in my own car. I think those are the seats that you went and checked out for Mitch Posner! If so, then thanks! Once a little goo was cleaned off they were almost perfect.
Couple of quick suggestions for your web page. On the 6-way seats, the seat rail does not need to come out of the car. In fact, drilling the holes in the seat rails is easier when the rail is left bolted down inside the car. Any metal filings can be cleaned up with a shop vac or a magnet.
Your web page mentions an electrical connection to the 6-way seats. In fact, the 6-way seats drop right onto the stock rails and there are no electrical connections. I suspect that you wrote this up AFTER you did the 12-way installation and you had wiring on the brain. Or, perhaps, it's because you removed the seat rails from the car and then when you put them back, you had to reattach the electrical connector. As I mentioned above, this is an unnecessary step.
I found it easier to mount the seats to the rails by mimicking the stock holes with the new holes that were drilled closer together. In other words, the front holes were slightly larger than 5/16" and the rear holes were shaped with a couple of files (rattail and triangle) to match the rectangular opening of the stock Impala rear holes. That allows you to attach the front bolts first, then, any slop in the manufacturing tolerance of the seat is taken up by the rear slots. I did my first seat by just drilling the four 5/6" holes as you described. Because the seat was not perfectly built (or perhaps my measurements were slightly off) the last bolt did not want to go in straight.
The shaping of the rear holes with a file adds about 10 minutes per side to the installation. But leaving the seat rails in place inside the car gives you more than that amount of time back. Thought you would be interested.
Thanks again for going to the junkyard to check out the seats that ultimately became mine.
Dave (written 9/7/98)