I have been looking around and David Gilmour used a BOSS CS-2 pedal That's now out of production. Along with about 50 other pedals hooked togeather. So thats pretty much out of the question.
The only effects listed on Opeth's site is BOSS multi effects boards GT-3 and GT-6.
The Korg multi effects pedals look my best bet thanks for the link fly135.
And i found this site through gilmourish.com
www.buildyourownclone.com building your own pedal sounds like a fun project. But for something you have to build youself they seem a little expensive. Still cool though