There's nothing wrong with the Visierschild you've included. It's a late pattern one but there's no reason why you wouldn't see it on an early pattern mount, particularly on an Sd.Kfz 10/5.
The only suggestion I could make with the Flakvisier assembly is to just make it the complete late pattern Flakvisier 38a by bangin' this faceplate on it if you have one.
Way too much work to turn the whole assembly into a Flakvisier 38 and there's no reason why you couldn't have the later pattern Flakvisier on an early pattern mount, mounted on a mid to late war vehicle.
Does anyone even make a Flakvisier 38? I noticed those two kits, with the 251 mounted Flaks you featured at the beginning of this thread had some vague semblence of an early shield, what are their Flakvisier assemblies like?
Allan