I have 3 Grizzly bows now.
The 1969 AMO 56" had a replacement endless loop string (my guess is an AMO string purchased from a store). With that string it was almost a 9 1/2" brace. When I used a flexible tape on it, the measurement was actually 57" nock to nock.
The 1971 AMO 58" had a string on it that braced out at almost 9". The string looked to be original, but there is no way to tell for sure-it did have the original rest and strike plate on it. It actually measures 58" nock to nock.
The 1973-74??? Super Grizzly is 58" AMO had a string on it that braced out at 8 1/2", also looking original, but no way to tell for sure. I had some tell me that it was a great shape original, but someone else told me it had been refinished. I personally don't think it had been messed with or shot much. It is 58" nock to nock.
I made new flemish twist strings and have them all at around 8" to 8 1/2" now. That seems to be a good brace height. Nice shooting bows.
RonP