No Luck -
I would say this is a valuable rig.
Your "Snail Drum" magazine (proper name Trommel Magazine) is worth about $1,500 to $1,750 all by itself (in my opinion) if it is not a reproduction. Looks like it is a Type II Trommel. Look on the back. It should have a letter "B" on top of a line with a letter "N" under it. And there should be a serial number under the "N" too.
Suggestion: go to
www.fgsfirearms.com or
www.gunbroker.com (for example) and see what dealers and sellers are getting for this kind of stuff. For example, FGS has a British proofed 1914 Efrurt artillery for sale now, that is listed as 95% finish, and they want $4,250.00 for it. (But you still need to verify what kind of proofs your example has, etc.)
Keep in mind that you need to understand the "retail" and the "wholesale" prices too.
If you mean that you have found 3 parts that don't have matching serial numbers, then yes, that does pull the value down as far as being collectable.