my 1971 chevelle originally came with bench seating how do i drill holes for buckets?

You need to acquire the stamped brackets for the inner mounts for the buckets. This is for both sides. Believe the outer mountiing points for the bench are same as the buckets. Those inner bucket brackets are a reproduced part.

You need to acquire the stamped brackets for the inner mounts for the buckets. This is for both sides. Believe the outer mountiing points for the bench are same as the buckets. Those inner bucket brackets are a reproduced part.

Best to get the correct 4-piece kit
I'm pretty sure all are the same from 67-72

The bucket and bench seats mount in different holes on outboard rear pair of holes.
The (with correct seat track) front oputer hole would actually be 1/2" forward and 1/2" inward from the original hole-------not to mention that 3 of the seat mounting positions are studs and not holes.

Have a look at this:
http://www.chevelles.com/forums/showthread.php?t=192782

I used 68 Buick GS seats, 68-72 mounting brackets, into a 66 Elky
I also measured a 67 GTO with factory brackets and the 68 Buick and got the same measurements.

Bryan