Cant answer your ? definitivly.A string builder may be more specific in any nuances who has used both B-50 and B-55.
But the main thing your looking for is some give to the string to protect the tips in general and particularly during a dry fire situation which is why B-50 and B-55 or recommended for vintage bows specifically by many archers.I believe in that quality of B-50 55 on Vintage bows for sure!!!
I have used many B-55 strings and B-55 and they feel and shoot pretty much the same to me as far as noise,feel of the shot and that forgiveness in the material that protects older vintage bows.
I would say its fine for your older Bear and I have used it on my older Bear limbs quite a bit.