Calico gatling kit with two M1s...opinion on value?

[Amtrak23]

What would something like this be valued at? Not shown is the original mount/tripod, and some extra banana clips with larger capacity. I don't have any better pictures currently or serial numbers, etc., but it is in very nice shape and shows little to no signs of use.

What should I look for or what do I need to be concerned with. Also would this be a reasonable item to hold on to as an investment piece?

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