heres some of the bracing ...
I just used what I had laying around but found that electrical conduit works well ,just smash the ends flat and run a 10mm drill screw it.No need for welding.You'll also need a screw at the intersection of the X.
You'll want to replace or repair any worn hinges first then adjust the door gaps.
Put your braces on the inside of the jamb so you can open and close the door ,this way you can monitor any movement when your cutting and welding..
The bracing I did here is way more than you'll need because I replaced the floors and rockers also dropped the body over the frame..
if your only replacing the floor theres no need for a brace connecting the front and rear pillar ,the rocker will do that.All you really need is an X in the jamb but extra bracing never hurts.
Send pics of your progress as you go...