If 1964 production, there are actually some quite collectible variations in the .357 Blackhawk. Called "transitions", the first production after the flattop had the protective rear sight ribs, steel ejector housing and steel "MICRO" marked rear sight. Then Ruger transitioned out the steel housing for an aluminum one, and shortly after that transitioned out the MICRO marked rear sight for an aluminum version not marked MICRO. Then Ruger changed the serial number height from small (1/16") to large (3/32").
After that Ruger got in a few more MICRO marked steel rear sights from a cancelled Colt contract and they used those up on any SA they happened to be making at the time.
Then finally, Ruger changed the barrel rollmark to include "INC." in the address.
So if 1964 production, chances are you are looking at a pretty collectible .357 version, with box starting at at least $495 and going up to maybe $600 with box depending on the demand for the variation.
Of course, your call at 95% is always speculative also, but generally when somebody is saying 95%, the grade is very conservative.
Send me a PM with the full SN and I can tell you a little more about the variation that it might be.
Chet15