I suggest caution in regard to putting the buttstock on the floor when driving out the tube. You may end up with a cracked stock. I'd suggest just holding the receiver in a gloved hand while you drive the tube into the receiver with a rubber mallet. A few really good whacks straight on the tube cap should do it.
Before driving out the tube, you should also put a witness mark on the tube and receiver, to enable you to line up the tube exactly as it was originally, so the op rod slot lines up.
I use a slide hammer arrangement that I made for this job. It fits on the tube, and I use a large brass washer to cushion the impact againt the mag tube cap. This taps the tube with new throat, or throats (early guns are two piece, might be interchangable ?), back into the receiver. I made it from a tin can that I poured lead into, with a mag tube sized clearance hole in the center. Good luck and Safe Shooting! _"gunsmither"