blues? like the say, just play it like you mean it.
blues tone is very wide ranging.
you got guys using LP's, SG's, V's, ES-335, Strats, Teles, and whatever they can get their hands on.
so anyway, the regular '57 classic is good enough for the bridge.
AFAIK the only gibsons that have '57 classics are all SG's.
SG '61 reissue & SG Supreme (classic in neck and bridge)
Angus Young model (classic in neck only)
and SG-3 (classic plus in bridge, classic in middle and neck)
what guitar is it going in anyway?
btw, get a SG-3 if you can, its a damn good value and priced the same as a SG Standard.