Easiest thing would be to replace the T350 with a 700R4. If you look around some, you can find one the same length as the 350, and not have to mess with collecting all of the clutch linkage, pedals, new bell housing, flywheel and clutch. The auto-auto swap would get you some better mileage, and save some money on the swap, as well. Converting to a stick may not be too hard, if you can round up the right parts, but by 1973, most cars were automatics - finding the correct parts to convert your car will be a serious challenge.