How tall is your dad? That is a huge bike and probably has a long top-tube as well, which means for an upright position the existing stem with ~10 cm of forward extension is working against your goal.

FOr maximum choice to stems the best thing is to get a 22.2mm quill-to-threadless adapter, which will allow the use of modern clamp-on stems... which every LBS has 100s of in stock.