hello rick,,your dads pistol was made in 1918 and is in a block of numberes issued to colt ,,so it sounds like the slides correct to the pistol,,value on these old 1911's has and still is going in one direction and thats UP
,,with that said i'd estimate the pistol if all correct with correct parts and with original finish on the metal parts to be worth around 1200-2500 depending on if how correct and the overall condition the collector see the pistol in,,if ya want to post a pic i'm sure nobody would mind ,,

,,sounds like you have a nice item and there very collectable these days ..
bigcurt