I just realized as of this month I'll have owned my BSA for 15 years! Wow, does time fly!
Anyhow, I'm in the midst of another rebuild (started by fixing an engine smoking issue, then obtained massive(!) scope creep) and purchased a chrome chain guard for my 1970 A65L (one of the weird 1970 Y bikes). A crack in the chainguard was repaired and rechromed before I purchased it. I'm unsure if a replacement strap was reattached at that point as well. My problem began when I fit the guard; the forward 3 bolt holes all lined up in their respective places on the swingarm. However, the rear strap isn't in line with the lower shock bolt, and there isn't enough movement to get it to line up. It's so off that I'm afraid of bending it.
My question, though: is the hole in the rear strap of the '69-'70 chainguard supposed to be big enough to fit over the sleeve of the lower shock nut (p/n 68-4235)?
Yes, the hole should be big enough to accommodate the larger part of the shouldered nut.
I recently acquired a used chain guard for my 1970-framed A65 bitsa. The hole in the "strap" was the correct size, but it did not line up with the shock bolt. I wound up cutting the strap off and welding on a fabbed piece that extended down at the correct angle to line up with the shock bolt. I never did figure out why the chain guard was not "correct"; it did not have the appearance of having been modified.
My chain guard had other dings and wrinkles, so rather than re-chrome, I straightened and flattened it as best I could, roughed up the chrome, and painted it black.