Mounting New Buckets???

[79BIG10]

I won these off Ebay and I'm wondering how to mount them? Here's the setup- I have a setup of aftermarket seats in the truck now that the seats mount to a square tubing frame with brackets to fit the bolts in the floor. Now if I take off the old seats and remount the new seats on that frame I'll be fine. But if I can't change them out like that then I'm guessing time to remount some holes. If I do that then how do I mount the seats securely? Just redrill and use some grade 8 bolts, washers, nuts? I want these to be secure to make sure they don't move anytime. Below are the seats I won.