Welcome to the forum Big Luke.

It would be a great help if you could post some photos of the helmets to help determine if they are genuine or not.

However, from your description of the markings, it would appear that they are genuine but photos would still be a help in confirming this.

For your information:

The markings on the M40 indicate that it was produced by Quist (as you have stated) in Esslingen and is a size 66 shell and part of batch No:11388.

The M42 was made by Sachsische Emaillier und Stanzwerke A.G. in Lauter and is a size 64 shell and was part of batch No:3428.

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Regards
John

"It is always wise to look ahead, but difficult to look further than you can see" - Winston Churchill