That’s getting pretty early for the black plastic grips like that. I know for sure late ac44’s to ac45’s had them sporadically. I’ve looked in my P.38 books and from what I can find is that Mauser started issuing pistols with these black plastic grips mid 1944. So, your ac44 a block is early ‘44. So my best guess is that your a block is a tad too early for them. It would be more correct with a set of reddish (6 broken lines at the grip screw) type grips on it than the black plastic type. The p38forum guys may know the approximate serial number range for when Walther started using these black plastic grips, Might give them a ring and see.
PS: Nice pistol!