I only have a rudimentary knowledge of Colt's, but I'm going to go out on a limb here and I'm sure I'll be corrected if I'm wrong.
It has a flat mainspring housing which makes it a 1911 rather than a 1911A1 which has an arched MSH. It's a civilian model. The serial number puts it at 1918 manufacture. I don't think the front sight is original.
More knowledgeable people will be along and will give you more information.
If you found that pistol in a garage, it is a fabulous find! (I also hope you found in legitimately) Do not shine it up or change anything or use a tool or anything else on it. Leave it alone unless you know what you are doing. Screwing around with it will destroy it and any collector value it has.
If you know how, just clean and lubricate it.
“If ye love wealth better than liberty, the tranquility of servitude better than the animating contest of freedom, go home from us in peace. We ask not your counsels or arms. Crouch down and lick the hands which feed you. May your chains set lightly upon you, and may posterity forget that ye were our countrymen.” ― Samuel Adams