I just installed the same seats in my 68 this past weekend. Easy to do.
I had to drill 6 of the 8 holes. It was difficult to get to the front outer holes for the position I had to put those slide tracks in to clear the gas tank. So I welded a 1/8" x 4" piece to the bottom of the slide track where the bolt hole is, and then marked them through the original holes from underneath. Then used the original botls to fasten it. Yeah, I know, 1/8"
sounds like it is too thin for seat brackets, but that is exactly what is used for conversion van seat pedistals and underbody reinforcement hardware. I have several kits for each of the Big 3 manufacturers, and in all their testing, 11 gauge is the recommended material for this application.
I spent a decade building custom vans at Vanworks in Fort Coillins, so I had access to the underbody washers (reinforcement plates) that are DOT approved. I used 1/2" grade 8 bolts on the four inner holes (where the seat and center console bolt down), and 7/16" bolts on the outer rear holes. A 3/4" socket won't fit in there, that's why I used the next size down.
Also, before welding the flat bar onto the slider, I ground of about an 1/8" so the seat would stay level and not raised up on that corner.
Drilling is no problem, as there is nothing in the way below the floor.
