You could try a larger tap and rethread the hole. I'd check the American Standard thread sizes as sometimes they work out well as they end up being "half sizes" for lack of a better term.
That might get you what you need withing going too large or you may be able to re-tap without drilling (sometimes we get lucky
). You never know unless you give it a shot. Given the length of the tread I'd use "fine thread" if possible.. It doesn't take much pressure to hold that rod in place.
If you want be real McGuyver you would place a ring/collar on either side (drilled and tapped) and lock it in that way. Personally I"d re-tap to a larger size or replace the fitting if possible. Good Luck !!
