Doug's headers not fitting - frustration

My headers fit fine on my 66 barracuda 360 magnum. My problem is finding a drive shaft to fit the 8.75 rear and the 727 tranny. If anybody out there knows of one or has one please let me know. The pinion in my old rear is 30 spline and the new one is 9 or 10 spline. I haven't counted the new pinion yet. Any thoughts out there would be greatly appreciated. Thanks