Hi Stoney,
Welcome to the dark side.

No reason why the Yamato barrels from Lionroar wouldn't work for your Mushashi, same goes for a lot of the other things in PE sets. There were a few minor differences between the two ships but nothing too awfully significant in the small scale ship lines. Tour about the model ship sites galleries on line and you will find a lot of good detail information as well as pictures to aid you in your quest for your battlewagon.
Don't be bashful about asking questions, we are a pretty gregarious lot here and I am sure someone will be able to help you out. Good luck on your project and send in your photos, we are a lot of lookie lous here.