hello i have a 340pd revolver and the more i own the gun i realize how much i would prefer the shrouded hammer over the centennial model that i have do any of you guys know of the price for smith and wesson to swap my titanium cylinder over to a minty 70's model 38?

Your 340pd titanium cylinder will not fit into the cylinder window of a "minty 70's model 38".

__________________
Ret. LE, FA Instr, S&W Armorer

oops huge brain fart on my part i forgot about the magnum j frame change

ALSO i did have a TYPO the gun is not a 340 it is a 342 38 special sorry for the confusion i am sure the cylinder is still just as long as the 357 cylinder because of the new magnum j frame change

FWIW, when the cylinder will fit the frame:
Smith Performance Center did my 25-5 45 Colt this year, charged me $95 for the cylinder, which was a slightly different color bluing, only noticeable if you really, really look for it, and $45 labor to fit it, plus very reasonable round trip postage.