You can take a 20 bolt pan and drill it for the different bolts as long as you have the pan on it to mark the location. Just drill and tap it and you should be fine. Earl Brown's done this a few times when he' needed a 14 bolt cover and only had a 20 bolt cover.
Here's a link to his timing cover mods BTW.:biggrin:
GBody Parts has the front cover you are looking for. 14 bolt and modified for better water flow as well as oil flow. GM cover and it won't leak!:biggrin: