I drained what was left for fuel and used a cold chisel to cut off the old filler neck. Was slightly concerned about sparks and vapors, but I went for it anyway. Worked pretty damn good and was off in just a few minutes.
Heated up the solder and pulled off what was left of the tank from the unreplacable filler neck. Rumor is the neck on the replacement tank is brazed on and should be swapped by a professional shop. I'll be looking for a radiator shop in the southeastern MA area if anyone knows one. Don't seem to be many around any more.
Rubber vent lines and filler hose are pretty much shot. I'll be replacing all of that when I put the new tank back in. I'll be running an external Walbro pump and vette regulator with factory style nylon lines and quick connects. Should have gone with the 87 style tank, but I already had the LMC tank from before I started the swap. Hope it works!