Arggh..Michael, I was getting myself all psyched for the ultimate SDC mods on my 604s and then got to the end of the description on the website and see that you can't do the 604 because there's not enough room due to the switches?

You can't do the electronics mod either eh?
So the only mod you do for the 604 is the hidden 84 capsule mod? This may be a tough question to answer but have you compared the sound of the 604 with just the capsule mod to the the 603 ultimate?
I guess if I were you I'd say it gets you 31% (69/219) of the way there