The RC4558p TI chip is really a fantastic sounding op amp. I've been modifying pedals using that chip for about two years now. Keeley uses metal film resistors, and capacitors. I use the metal film caps, but i also give you a choice of resistors to use. Each having it's own characteristics.
there are alot of users around here that have keeley pedals. I'm sure several will tell you how well they sound.