maxumcustomercare.com does not list a 1900SC in 1999, but a 1900SR had a 14-1/2 x 21 prop from the factory. In 2000, depending on which 5.0l motor is in the boat, the factory prop for the 1900SC was either a 14-1/2 x 21 or a 14-1/2 x 21.
Most props have the part number stamped on the body or the prop pitch stamped on it. Using the current prop pitch and your wide open throttle (WOT) RPM, you should be able to figure out if you are over-propped (Pitch too high, resulting in low WOT RPM) or under-propped (Pitch too low, resulting in a high WOT RPM). Recommended WOT RPM is listed on the air cleaner cover. (A google search shows it should be 4400-4800, but go by the specs on your motor). Hope that helps.