Just got out to the garage for the first time in a few weeks yesterday. Did some more work with the subframe connectors, and more today. Ended up drilling 1/4" holes every 3" or so down the sides of the rails, then pulling the floor up with a self tapping sheet metal screw. Drilling in the middle wouldn't have worked due to the floorboards being pretty messed up. Driver's side is ready to weld on, passengers is in much worse shape, so I figured I'd leave that one for last. Hopefully lessons learned on the easy side will translate to the hard side. Here's a pic of the floor pulled up reasonably well under the rail.
Also got new front sections for the rails from John @ BD. They look like they're going to work. Basically they're just like the rail on the bottom, but without the flange on one side so that they can be welded to the rail in front. After I get the connectors connected to the floor, then I'm going to mock up the TC area and then I'll try to do the connectors to the TC square tube, and those pieces to the frame rails all at once. Also notice how flat floor sits against the rail here.