Although I think the story is highly unlikely, ( with the breakup of the Soviet Union and the opening of archives, I think It would have gotten out somehow).....However as for plausability; the top Soviet Fighter-intercepter in 62 was the MIG-21 Fishbed, Top speed; 1385 mph, ceiling: 50K ft vs 1325 & 64K ft for the Hustler........Sneak over Moscow under the radar at 700+ mph then climb to 64000ft and accerate to 1300 mph...In 62 the Hustler would have been real hard to catch flying two and a half miles above the soviet intercepters....It could also outrun SAMS..Powers U2 was only going about 400 mph when hit.....
I remember that, it was hilarious (from a safe distance).