If you have your heart set on running an original carburetor on your Durant with a 14L or 15L there is a rebuilt Sp-13B on Ebay. Starting bid is $100, but it looks like it's in good condition. Most of these self destructed because of the pot metal they were made of was of poor quality. This is probably the best one I've seen. Just search Tillotson SP-13B. GOOD LUCK!