Your gun also has a 1911A1 arched mainspring housing and long trigger, which are not consistent with a 1918 gun.
If it were all complete, and frame matched to a Rem-UMC, it would be worth perhaps $3,500 - $4,000.
The early guns are not really good shooters either, as parts were fairly soft and won't hold up to high volume range use.
As it is now, its value is the sum of its parts to someone trying to complete either a mismatched Rem-UMC, or Colt from that time period.
I would put a rough value of $850 - $950 on that one.
rc