Hey Andy, happy to help but need more info in order to do so. What is rubbish? Are we talking speaker installation? Are we talking hard wire routing or bolstering cables? Tell us what is wrong in your mind and or post pictures and what need take place for it to be right by you.
Until I have a better idea of what the issue / issues are I can't offer much help. You mention "Old helmet" now does that mean we are talking about 3 helmets, two new and one Old. Just need more info.
Let me / us know and I'm sure we can make it right.
In the end I'm sure once we / you get into it with the right guidance / benefit from the experience of others we can work it out. You won't need someone else to do it for you.
Thanks
Studley.