Hopefully you have 68+ long axles and 4 lug drums, or it's a 68 autostick pan with a 4 speed?? If so, you could redrill the drums, but you're going to need a really thick spacer. Because of that, an adapter works for you.
At the front, do not waste your time with a narrowed beam. Not only are you not going to need that, you're going to need wheel spacers too.
If you want to check things before you spend the $, do the disc conversion and bolt the bare wheel onto the drums and rotors to see where it lands compared to the outer fender edge.
