If you look at the seatbelt mounts, they are actually bolted to the floor with a reinforcing bracket underneath that bolts to the chassis. It is held to the bracket on the floor with a pin with a tiny split pin through the end.
I would imagine that if you fixed the front end securely as far as the seat belt mounts, then made the rear section removable you wouldn't have any problem.
I did spot on ebay last night you can get floor repair sections now, which would make this option a possibility without butchering a new floor.
And yes, they can be bolted/riveted into place as they are not classed as structural due to the separate chassis construction. Technically only the sills and rear crossmember are structural items