I have a couple of old Carling Hoff-Stevens kegs (a.k.a. two prong taps). I cut the top off of one of them and turned it into a keggle for my boil pot. I actually like the shape of this better than a Sankey keggle because of the curve at the top helps prevent boilovers and the dish shape in the bottom makes it easy to whirlpool the trub into the center.
I made a pickup ring for the bottom out of 3/8 copper to fit the outer ring and it does a great job of picking up clean wort after stiring up a good whirlpool and letting it settle. A little stainless scrubby stuffed in the pickup tube groove keeps all the trub in the center dish. A couple cheap gate handles pop riveted near the top and you've got handles too!
To plug the side bung hole just get a large wine barrel bung from your local HBSH in either rubber or silicone to fill the hole. I got one with a airlock hole, inserted it from the inside, and used 5/16 SS bolt and wingnut with a piece of plate on the outside to make a leak free plug. Don't worry about heat as your burner can't get the SS keg that hot that high and the rest will never be hotter than boiling. I've used mine many time with no problems with the plug.
BTW, if you're upgrading from an old AL turkey fryer pot like I was, the outside of the bottom ring make the perfect place to cut and have the AL pot lid fit just perfectly into the keggle.
Oh, and as luck would have it the same outside ring on the bottom perfectly mates with the ring on my burner base making it almost impossble to tip over when full, or at least with 10gal in it. It's a hole lot more stable than a Sankey on the same burner.
I wish I could take credit for planning all this out very carefully ahead of time, but it's just not the case. Anyway, I'll settle for luck. My homebrew club buddies think I'm lucky as s**t that it worked out so well given the stabiilty issues and wort clearing issues with Sankey keggles.
Here's a link to pick of my boil pot.