you two are to fast for me....
think the easyyyest thing to find would be a bung for a 02 sensor that they weld onto headers....readily available at any speed shop and designed to be welded....
have any old oil pan? if so cut the one offa it...grind ,prep and weld to tank
CAUTION...as per if you go this route yer welding on a gas tank...once tank is lined would give it good rinse with cold water before and after welding ect and drain and dry before welding bung on...liner product may be flammable and leave fumes in tank...when in drought ask questions....
dawned on me when l looked at yer sig and saw the wagon...from what folks are saying their non existent so putting a bung in is a good bet for future issues
... another thing ld consider doing if l were in your position is setting it up on bbq style aettup where you can turn it over like a rotisserie ...would then throw in half pail of pea gravel and some water and rock the crap outa it till all the rust ect has been knocked lose...then would clean out and then etch and coat....l do the same for cleaning inside of bottles and washer bottles ect...little bit of sand,water and shake..cleans them up nicely
when l took my tank out was great on the outside but inside was nassssty and couldn't belive the rust in there...was like someone glued pea gravel inside...it was that rough...anyway food for thought...hopefully someone here that's gone through it will pipe up with advise
quick question...am guessing the neck on this tank is non removeable unlike the 70 fury gas tanks which are?