Buy a tap and use the tap to chase the threads. . .quality taps (not the hardware store junk. . .not that you would get an 1 1/4" tap from the hardware store anymore anyway) are a good thing to have on hand!
Worst case scenario you can take an old heim (a bolt would be better, but I'm betting you don't have one that size lying around) and grind some flutes into the threaded portion of the body with a dremel tool to make room for chips/debris and use the make-shift tap to clean up the threads.
Those are the two easiest ways without a lathe. . .
Try Smith fastner out of Bell, Ca. They have a hugh variety of nuts, bolts and all kinds of stuff. Thats where we get most of our stuff for our machines. Both of the above mentioned ideas are the easiest way of doing that.
Do not use an impact to drive a tap through a bung. I had to remove a broken tap from a trailing arm becuase someone though it was a good idea. Not fun or easy............
Use good taping fluid like moly-d and a good tap wrench. A cresent wrench can be used it your crefull not to pull on just the handle, keep one hand on the tap when under load to keep it from cutting off center.
Take'm to the machine shop and have them cut the threads. I had to have 16 1 1/4 bungs recut after tig welding the bungs. I had left and right handed threads so the taps were more the than the machining.
The machine shop probably ran a tap through them which is why it would be so cheap. . .picking up pre-existing internal threads with a single point tool is not a fun or fast undertaking! Once you pick them up chasing the threads with a single-point is quick, but you can absolutely ruin a part if you don't pick the threads up perfect. . .