I have seen that stinger in Grabow and Kaywoodie but in Golden Gate and old Gourd calabash too. Personally i don't like it and i remove it but since you want to keep it we have a huge problem!
1) that ring is glued in the shank, if you try remove by heat it you may damage the shank very badly
2) the "face" of the mouthpiece aka Stem's Face is worn a little bit thus when you tighten it won't fit exactly as it did from the factory, this happened because the previous owner was careless and pushed hard to the right the mouthpiece each time
It's very difficult to work inside the bolts of the shank, each time you have to work by a quarter, make a test, not fit, again block a quarter of the bolt, test, not fit, again....etc till you find the perfect point.
You can to the opposite work on the mouthpiece but this is a "no turn back" work, one mistake and the mouthpiece may fit but the stamp will be in wrong position looking the sky.
If you still want to keep that stinger and mouthpiece i have something to suggest:
Remove by heat and gently the stinger from the mouthpiece
Clean the stinger from old glues
Clean the bolts inside the shank
Tighten the stinger alone inside
Work gently inside the channel on the mouthpiece but NOT too tough, don't make the channel too wide
Have ready an epoxy glue plus a cyanoacrylate glue
Clean with high grit sandpaper the "face" of the mouthpiece but gently, make a test if fits properly, if not work till you get the perfect alignment
Put a little bit of epoxy on the stinger and one drop inside the mouthpiece and push it to the stinger
Make the alignment and keep it as is for few minutes, push it good and wait.
The cyaoacrylate will keep the mouthpiece where you want it [the stamp is horizontal] and will accelerate the work of epoxy which will make the stinger glue hard
Don't put too much of epoxy because will come out and make the things worst and don't waist time after the use of the cyanoacrylate, push and immediately hold it tightly and wait few minutes.
Finally take a look the pipe in "profile", if everything is OK then gently put somewhere the pipe vertical and wait overnight to dry. I insist in vertical and don't touch the mouthpiece till the morning!
I wish you the best.
