I'm converting my 72 from bench to buckets, but want to put in the adapters for factory buckets, and make an adapter plate for my modern seats that are comfortable. Could someone please let me know what the bolt pattern is for factory 68-72 seats? I have heard 13x15 inches but cannot verify without a factory seat. I found the following threads that were reasonably helpful, but still not what I wanted.https://macc.chevelles.net/buckets_install.pdf

http://www.buickperformanceclub.com/buckconsole.htm

 

The way that I do it is first buy the 4 piece bracket set (one small bracket + 1 big bracket per side).
Bolt them to the bottom of your bucket seat track feet. (make sure the tracks are on the right way, single hole to the front double holes to the rear)
Remove the track return springs so they are easy to adjust. Line up both tracks so they are in exactly the same same position (72 is easy since both sides have detents)

There should be two holes in the factory floor in the rear outboard position on each side (i see you have a 72, SOME 71/72s may only have one hole drilled, but there will be two nuts welded to the support brace under the floor, so if only one hole in the floor, check under the car to see which position it is in.

Bucket seats use the INNER of the two floor pan holes in that rear outboard position.
The OUTER rear foot hole in the seat track bolts to that INNER floor pan hole (confusing, but its important to get that right).

Bolt the seat in place using that rear outboard bolt attached to the floor.

There is a "Step" In the floor pan, that falls right before the spot where the FRONT feet fall.
Position/adjust the seat so that the fronts of the two brackets are roughly lined up with that step in the floor pan.

Your seat is now squared up... Take a welder and tack a couple spots to hold the brackets in place, remove the seat and then finish welding.

Repeat on the passenger side.

FWIW, this process is much faster if you have a bare lower seat frame you can use as a jig.

** If you use the WRONG rear outboard floor hole, the seat won't be able to line up along that step in the floor pan ahead of the front feet, and it will have the outboard side of the bucket seat touching/rubbing the seat belt retractor.

hope this helps, sorry i don't have any photos on this one!

 

Ok, i lied, i found some pics... I highlighted where that "step" is. I use that to square up the seat, with the only fixed position being that rear outboard pivot point.

Highlighting the step

Unmarked * Pass side brackets are just sitting there, not yet tacked into place.

Using a bare lower seat frame to set the positioning... Note the two holes in the floor pan for the rearoutboard position. The OUTTER hole in the track, is bolted to the INNER hole in the floor.

 

Thanks, what I really want are the LxW dimensions of a factory bucket. I don't have one to set up the bracket positions. I have ordered the adapters from opgi.

 

I have another pair of buckets arriving next week.. I can get the measurements for the 4 holes for you at that time if nobody else has by then.