Bill,
I think you have an amalgamation of maybe some original parts and later parts made to complete what was left. The barrel may be real, but like Ron suggested, we need to see photos of the barrel.
I think you need to consider a return if it is possible. If not, learn from what there is to learn and then research your next purchase. I just purchased a tanegashima from an online auction. I used what I have learned from Ron and Piers, along with Ian to make an educated guess, and while it too is not a "eye catcher" it is original, and I am sure I paid way less than yours.
If you own it, there are worse things to own, and I want you to know that Ron is being fatherly and trying to help you understand. He, Ian and Piers are all western experts on this subject and if they (he) says it is not correct, you can bet on it.
Ron has forgotten more about these things than I can ever hope to know.
Good luck, and welcome. I hope this does not put you off of your journey for true Hinawaju (Fire Rope Guns)