Sounds like you have an easy decision. But please recognize, even in its present condition you can still hurt the originality. When you say 1955 (I presume a 5 Screw) vintage which indicates you can go with either the satin or bright blue.
The satin may be the harder of the two to replicate properly so you might as well go for the bright blue. Smith will refinish it and you'll get a quality re-finish but you'll get the current blue which is different from the 1950's bright blue. So someone like Ford's who can replicate that period's polishing technique and blue would be a must.
Just any local blue job, believe or not, can still drag down the gun's originality and appearance. So please beware, most re-blue jobs may shine and 'look' nice, but improper surface preparation can do irreversible damage to original contours, rollmarks, edges, etc., etc.
Personally I'd rather have a basket case then an improperly done re-blue. You really don't want a re-finish, but rather a finish restoration. Because you got the gun cheap is not s justification for a cheap re-blue. It's a better justification to pay a little more and have it done correctly which you are obviously concerned about or you wouldn't have asked which finish would be correct for the period of the gun.
Hope that helps,