Sounds like he's using a harmonizer of some sort. My guess would be the ElectroHarmonix POG (the big one). My dad is a big Leslie West fan and it's rubbed off on me through him. I love Leslie's vibrato and of course how he's after the big tone. The only thing I don't like about him is the fact that he started the whole craze for the Les Paul Jrs. If it wasn't for him you could pick up '50s Jrs real cheap! I admire a guy who could make a "student" guitar sound like that!
'67 and '74 Fender Twin Reverbs, '74 Marshall 1987 lead mkII, Metro Superlead 100. Pedals from TC Electronic, Ibanez, Dunlop, BK Butler, Electro-Harmonix, Fulltone, Maestro/Gibson, Loopmaster switching, VoodooLab, Boss. Gibson and Fender guitars, Dimarzio pickups.