Yep drill out the spot welds. Get a blair rotobroach, awesome tool. Takes a bit to get it right, but, works like a charm.
The area that the rear of the floor pan and rear seat area has a few bead welds that need to be ground down/off.
Once you think you got them all, there will be some that you never thought exist. Ones that nobody ever seems to find attach to the rocker panels in the rear footwell vertical walls. There are about 20 on each side.
Once you cut the spot weld, I take a stainless gasket scraper/Hammer and make sure it's loose. Sometimes you get the weld drilled about 90% and need to cut the rest. Then pound it back flat.
It will take a few hours to get the pan out, but, it's worth it compared to the nonsense of splicing a bunch of pans in.
If you hadn't planned on it, while you're in there, treat the insides of your frame rails with something like zero rust.
If you have an air chisel, there is supposed to be a bit on the market that will split spot welds and not tear up the surrounding metal. A buddy that parts a bunch of cars told me about it, but, hasn't got me any more info.