Some times you can get lucky,when I needed a driveshaft for my '54 with a 302/AOD I was able to use a '86 Crown Vic shaft and a NEAPCO conversion u-joint and it was a bolt in.Since you are using a C4, a shaft with an AOD front yoke will interchange,so if you go to a driveline shop(check yellow pages) they can tell you how to measure for the correct length,most will have a large pile of used shafts to choose from also look for a wrecking yard that specializes in Fords' as they will probably have a rack with nothing but driveshafts in it,you'll be surprised how much you can save using a measuring tape.