Brace height should be in the range of 6-1/2 to 7". Before '59 the Bears all had the standard "fistmele" brace height. Most of mine are pleasant at 7" or just a hair over.
A lot of the '57-58s I've had/seen had pretty blocky tips. Those had a bit in the way of handshock. The ones where the tips were reasonable (more like the '55 and '56s I've owned) shot very nice. Any that I'll be hunting with will have their tips reduced, collector's value be damned
What I've been calling a "'57" has almost a full inch more reflex than a '58. They are a little touchier to shoot and tune in my experience, but faster # for #.
An overbuilt dacron string is going to be a little shocky on all of 'em. I've been using 12 strands B50 strings on everything up to 60+# at my 30" draw. I don't trust dacron to go with fewer strands, but ymmv.
I must say, my '58 Polar with a relatively skinny TS-1 string is very nice to shoot!