Someone on challengerforums posted this "guaranteed" information:

Initial launch includes the V-6. It will be priced below the comparably powered Mustang.

One other engine available at launch: 6.1L Hemi with 435HP (not a typo - that's a 10HP rating jump over the current SRT-8).

Price of the 6.1L Hemi will be under the price of a convertible Mustang GT.

The "Big Engine" will be "available in '09."

Confirmed colors at launch are:

B-5 Blue
Hemi Orange
Sublime Green