First, drop the tank (it would be nice if it would drop straight down between the frame rails

)...
Step two, buy a new tank...
... (or just clean the old one

) I’ve done a few of these now and feel pretty good about my system. I even still have my face and all of my fingers :knocksonwood:.
I drain the tank of all gas, pull the sender, and connect my shop vac hose in the blow configuration (don’t want to suck fuel vapors into the motor).
Once it is completely dry, I fill it with one gallon of Simple Green, and top off with water, sloshing it around as I fill, and let it sit for a while. I then do another soak & slosh with soapy water.
Then I drain and do the shop vac routine again until dry. At this point, you shouldn’t smell any fuel vapors. If you do, repeat the above until clean. Or take it to a radiator shop and have them boil it clean.
Like Anthony noted, the 60 tank is set up for an in-tank pump. There is already a fuel reservoir tray located below the circular embossed area.
Before I cut, drill or weld, I put the shop vac hose in the sender hole (in the suck configuration this time) to keep air moving through. The idea that the fuel:air ratio is too low for sparks to ignite if any vapors remain.
Mark the center, drill a pilot hole, then drill the main hole...
There is a threaded split ring that gets tack welded to the inside of the tank. It just needs to be held in place, no continuous beads. First mark and drill the screw holes, and bolt the ring below with truss head screws while you tack it in...