Looks like a nice helmet, other than having the enlisted pattern front plate as you've already pointed out. That's an easy fix.
I trust that there are no extra holes in the helmet body behind the current front plate on the helmet?
From the photos you appear to know what you have. The wappen that is on there now is mounted too low and is broken. Other than the plate - it looks good. Finding a wappen that fits may not be all that easy. Officer helmets were private purchased and there were many makers, not all their plates were set up the same way.
That looks like a very nice helmet :-)
I would take my chances on that front plate, and take the patience to find one , if the price for the helmet is fair !
Wir kapitulieren niemals !
There are no extra holes and is officer's wappen difficult to find?
it's in nice condition.
You can normally find a Prussian Officer front plate on eBay.com from time to time. Someone just sold one a few days ago with the split pin attachment style for $50 (link: RARE WW1 Pierced Front Plate German Spike Helmet Pickelhaube Waterloo Cross | eBay), which was very reasonable. Another one sold for $45 that had the screw posts. (link: Prussian German Officers Spiked Helmet Plate | eBay)
As member aicusv mentioned, you may run into some fitting problems depending upon the spacing of the mount holes. Simply measure the distance between the holes, and ask any seller who has a frontplate for sale on eBay to measure the distance between the threaded screw posts before you buy a replacement front plate. That should prevent you from getting a replacement that might not fit in the holes.
With a little patience, you'll be able to properly complete the helmet. I hope that you can pick it up.