Did you ever wonder what kind of acoustic guitars they are playing on the tour? They're from Yamaha. The benefit is that you don't have to mic them and they still have good tone. You don't have to worry about feedback which is usually an issue with acoustic guitars live whether you mic them or use an acoustic pickup. link
According to the website,
"Elegant design and sonic solutions are Yamaha traditions. Yamaha continues to innovate with the Silent Series. Originally designed as ideal practice and travel instruments, the steel-string SLG100S and nylon-string SLG100N quickly became popular with touring guitarists enamored with its practical, feedback-free live applications and modern jet-age appearance."
I think Brian's 12 string for LOML and 39 is a Guild F512. From the pics, it looks like a jumbo body. link
I always thought Brian had an affinity towards Ovations in the early days.