For what it's worth, I'd definitely make it bolt in for now. Depending on the engine and transmission you swap in later you may end up having to completely redo it in the future.

The PO of mine had pretty much butchered the firewall and toe board so I was starting from scratch. The set back and height of my engine required a hump. When I did the original mockup on it I was planning on using a 727 and the floor didn't need much of a rise, that changed when I decided to use a 518.

I built my floor and new toe board out of some stainless I had laying around. I originally made it bolt it (I used nutserts and 1/4-20 bolts). As the mockup is pretty complete I eventually did go ahead and weld it in.

There are some pictures of mine in my build thread.

https://board.moparts.org/ubbthreads/show...part=1&vc=1