Hi, I am ready to weld this floor in on a 74 cuda. The floor doesn't lay flat on all areas of the frame rails. I was going to use sheet metal screws to hold it tight for welding, but before I start drilling holes through my new floor and the frame, does anyone have a better idea?

Can't you screw it down and then weld up the screw holes as you go along?

Uh, yeah, thats a better idea. Thanks.
I was going to drill a hole for plug welding every two inches, then screw it down about every 4 inches, or where ever it needed it. I hate to drill through the frame rails, thats my biggest road block right now. Maybe I'll drill a 5/16 hole in the trunk floor, then drill a 1/8 hole in the frame. Then use a sheet metal screw with a washer to hold it down, and plug weld the same hole I'm using to hold it down.

I just put a trunk floor in a '70 Challenger, and I REFUSED to drill the frame rails! I used the existing holes in the pan for access to clamp things up where I could, and the following idea: take an 8 foot long 2x4, turn it narrow edge up and wedge it under the cross brace at the top- in the corner at the inner wheel house. Wedge a short 2x4 under the long one to act as a fulcrum in the spots where you need to force the pan down on the rails. Have a helper pull down on the end of the long 2x4, or if you are working alone like me- hang some weight from the end. I hope you can picture it from my description.... sorta like a see-saw with a moveable fulcrum.