Moving bucket seat floor mounting back??

[my71gmc]

I the carpet removed in my 71 Jimmy, and noticed that there is a set of seat mounting holes a few inches behind where the bucket is currently mounted. I assume these are for a bench seat install???? Either way, I would like to move my buckets back into these holes (tall and could use more leg room), and would need to figure out the front mounting as it will need blocking up, drilling through floor, ..... Has anybody done this?? and if so, did it work well?? Thanks for any help.