The various Walther books don't seem to help much, but the accumulated opinions are that Manurhin pistols were the earliest post-war guns made, with parts manufactured in Germany and then shipped over the border to the French factory that assembled them and sold them on. I'd guess somewhere around 1954 for your pistol.
As for value and collectability, the Manurhin pistols seem to fetch less than the Walther marked ones. Some of my favorites are Manurhin PPK .22 pistols, which shoot wonderfully and are 50's guns. They were cheaper to buy than their Walther marked brothers, but no less fun to own.
I'd say your pistol, with box and all, maybe $400. If it was a .380, or .22, $600. .32 is the most common model. I say this, not from manufacturing records or books, but from years of reading, watching and buying. The Manurhin pistols will have pre-war compatible parts in them, such as the squared firing pin and square hole safety.
Some of the early examples in the same serial number range were Dural (Aluminum) framed, which might increase the value slightly. Again, most collectors will stick to the Walther marked guns, the same model of which will typically fetch more, in the same condition with the same accessories. But yours is complete, and should sell for more than a later, incomplete, and slightly used Walther PPK in .32, which people can't seem to sell for $400 lately.
Enjoy it, not a huge dollar value, but it's still the same model Walther PPK that James Bond started with (after they took away his Beretta).
