How to install bucket seats?

I am putting Sebring seats in my 65 Dart and already made brackets. I used L-brackets and slotted L channel from Ace. The later on the outside for the gap you mention. I used the 4 factory bucket holes, plus drilled 2 new holes further aft (w/ spacers) since the Sebring tracks are longer. I had to drill only one hole in the Sebring track, for each seat. The driver's and passenger holes differ in my 65 Dart, as I recall.

A store-bought kit would be nice since I spent most of a day on each seat. I set the old Dart seat upside down on an outdoor table, with the Sebring seat next to it to measure back and forth many times, moving the tracks back and forth, etc. I'll post w/ photos after I get them installed and prove it works fine (when does that happen?). A few months from now since currently painting and such.