The factory ran weld beads about 1" long approx 2"-3" apart. Then used seam sealer all the way around to seal it up. On my 67 notchback I just welded it all the way around. I have no intentions of removing it. As far as how to fit it, the back end bumps up where the inboard FWD bucket seat reinforcing plate is. Use that as a starting point.
It would also help if you cut the sheetmetal in the floor away just enough to do a mockup of your 4 speed trans with at least the shifter tower installed so you know how far to the right or left to position the 4 speed hump. I used 2 different colored sharpie markers when I did mine. I traced the outline of the hump on the floorpan in RED sharpie, so I knew not to cut on that line. Then I drew my actual cut line in black inside the red line. The nice thing about cutting it out is you can trim the floorpan to give you a little additional clearance under the hump. Theres not much room under it for the rods and tower. This is why the reverse hangs under the crossmember.
Hope this helps
Matt