I'm a fan of all stainless fittings for my kettles (plus keggles when I was using them). You do have at least a few options.
1. Leave it as is (of course).
2. Get a weldless bulkhead/stainless valve assembly (I'd get a three piece ball valve if you don't already have one) and then figure out a dip tube that works.
3. Get someone to weld in a 1-1/2" TC ferrule (go the larger bore version) and get a diptube that will work with it and allow you to also use a 1-1/2" butterfly (TC connecting) valve.
In the past, I've simply used a 1/2" compression to NPT fitting on the inside to 3 piece ball valve on the outside (with washers and o-rings to seal) and then made my own diptubes. I have a tubing/pipe bender that handles the 1/2" OD stainless tubing for that.
If you do go center of keggle (lowest point) and use propane burners, just be aware that you'll need to adjust the valve on your pump (assuming you have one) while the burner is going. Often done when sanitizing either a place or counterflow chiller before chilling the wort into fermenter.