I have seen the early "flat" front sight base with the UP in raised letters on a Colt SP1 in the 007xx serial number range. Barrel is stamped M with the Colt triangle under the front sight base also stamped 12 near the front on the bottom. This rifle is "new" and was purchased by a collector in KC years ago.

Could Colt have changed the front sight base during the early SP1 production?