Well, seeing as he asked, we might as well beat it some more. (Dead horses just piss me off; they just lay there, all glassy eyed, ignoring me. I know they're dead on the outside, but they're just laughing on on the inside. Insolent little worm-ridden carcases, anyway...)
Navigator, you may log PIC time when acting as sole manipulator of the controls, for the puroses of 14 CFR 61.51(e)(1)(i). However, you're ill advised to do so, under Part 135. If you'll review 135.109, you'll find that the certificate holder designates the pilot in command for a particular flight. The designated PIC remains the pilot in command for the duration of the flight.
Unless you are actually the pilot in command, you are best advised to refrain from logging time as PIC.
You made reference to an "ATP Type." The ATP certificate is a pilot certificate, and a type rating is a rating added to that certificate. If you obtain your ATP, you don't have any additional privileges in the airplane, without a specific type rating for the airplane you're flying. Additionally, unless you are acting as PIC in that airplane, a type rating isn't required.
So far as two pilots logging pilot in command time under Part 135; it's inappropriate, and serves no good purpose. Further, if discovered, it appears as though one is padding one's logbook. It can only make you look bad.
If you lack pilot in command experience, go get it; take a job in which you can be pilot in command. Many times I've known pilots who hired on with a company or operator with very low time, as SIC. These pilots spent ample time with the company to be able to upgrade, except that they lacked the pilot-in-command experience to be insurable for the upgrade. They had to leave, take a job doing freight and work up like everybody else, then come back. Many didn't come back, but the point is that you need to get that experience some place. Time building is worthless; get the experience to qualify, rather than attempting to work around the regulations in order to pad your logbook.
