Hello,
Congratulations on this excellent find!
I found one of these back in 2009 in similar condition. A family that lives about half an hour from me had it.
Unfortunately I sold it a couple of years later, along with 3 other enlisted pattern helmets, in order to help finance the purchase of a Guard du Corps Officer Helmet with Parade Eagle, which was also found in my state.
I have always regretted selling the Saxon helmet. The person who bought it from me sold it to someone else, and now I do not know who has it.
I do not see any dents in the helmet body that would need the use of your metal smith friend who worked for Tiffany. There is a small dent in the spike, which is definitely not detractive, at least not to myself.
My old helmet was similarly missing one of the M91 side posts.
Basically all that I see that needs to be done is the replacement of a domed rivet that would re-attach the wearer's right side of the back lobster tail visor, plus the repair of the one Model 1891 Side Post.
It can be argued either way as to whether or not you should polish/clean the Tombac metal body and the neusilber fittings on your helmet. If it were my helmet, I would likely simply leave it as it is, other than having your friend repair the missing domed rivet that is now missing, in order to hold the lobster tail rear visor back in proper place. It's also possible to have the one Model 1891 Side Post repaired/replaced that is presently damaged/incomplete on your otherwise fine helmet. I myself might consider finding a correct style, exact size original liner to place inside your helmet. But not having a liner in this helmet is not the end of the world. It will display nicely without anyone knowing the liner is missing, until the pick the helmet up to look inside.
Here is the link to comments posted about my former helmet from back in 2009. Unfortunately the forum was using outside hosting for photos posted here, and the former photographs are now lost on my posting because I had used the old "photobucket" to host my photographs. I can look amongst my old photos on CD-Rom here at home, in order to locate the original photos I posted of my former helmet. I should do this to properly restore the original thread posting.
The link to comments on my old helmet:
https://www.pickelhaubes.com/xf/threads/a-suprise-early-christmas-present-to-restore.4675/
Best Wishes,
Alan