Custom Shop: How Custom?

[mafoofan]

Apologies if this has been covered already, but I've been searching and haven't found a full answer.

How extensively custom a gun can the Colt Custom Shop make? Are they limited to modifying customer-supplied, already-made Colts and current production models, or can they do a fully unique 1911 from the ground up?

Also, in terms of workmanship, how do Custom Shop guns compare to regular production guns, as well as those made by the best semi-custom (Ed Brown, Wilson, etc.) and best custom (Lieberberg, Chan, etc.) makers? Are the internals standard factory-grade, or are they finely hand-finished?

Thanks!