If I still had this gun in shootable condition today, would I recommend these loads for it, Definitely NO? I do however have to say it never squealed or groaned while they were being used. It is I suspect quite likely this late-model heavier gun than the 5-5 lb earlier models had thicker sidewalls, though I never had on of the light ones to compare.
I'd agree that the later, slightly heavier Flues guns would likely be less prone to suffer a cracked frame. My first American classic was a Flues Field Grade 16. I don't remember for sure whether I had the chambers lengthened (well before I learned it wasn't a good idea) or whether they'd been lengthened by a previous owner. But I shot high brass 1 1/8 oz pheasant loads in that gun without issues. Like you--and even though the serious Flues problems reported seemed to be with the very light 20's--I would not do that again. (Instead, I'd look for an NID 16ga!) But it survived just fine.
