[DonVoigt]

Thanks for the pictures of Art making the frame mods! Your 1906 upper looks fine too.
Not unusual to need two side plates to make two different uppers function with the same lower; those pesky tolerances again.

I will be very curious to know if you can get all 3 uppers(the 3" when you make it included) to function with the same main spring.

The shortened frame makes for an exacting job to get the mainspring the correct length and strength. My 3" 7,65mm upper and the bull 9mm will function with the same mainspring; but it took a while and cutting several springs to get the "right" one. It also takes Privi or hand loaded 7,65mm to function- fiocchi just won't work.