Hi Hughsey, as the saying goes: "anything is possible". RS will indeed have nearly everything you need to build it, and if you can make one as good as, or better, than your Arcam then I'll buy one off you.
You'll need a bit of help though, I just did a quick search on Amazon and came up with this book: High-Power Audio Amplifier Construction Manual: 50 to 500 Watts for the Audio Perfectionist by G. Randy Slone, which might point you in the right direction, but have a good look around for other books, like I said I only did a quick trawl.
A friend of my father made one several years ago, it sounded pretty good to me, don't know if it's still going though.
Good luck with the project, I'll be interested to see how you get on.