Do not attempt this without a tech manual backing you up , most Libraries have Chilton's Manuals ( big thick hardcover ones , not the "mustang only " things ) that you can photocopy the distributor placement and firing order pages . Find #1 cylinder ,mark that spot on the dist. body and the intake manifold, take off the dist. cap and crank the motor until it points at the mark you made , loosen the dist. clamp and pull it up , notice where the rotor ends up , that will be your start point for the replacement dist. . Slide the HEI in and you should be lined up , put the wires on the correct plugs ( the old ones are incompatible with the HEI .) and start and time the motor . If that did not make sense , DO NOT attempt , it is easy to screw up , have a shop do it or get a mechanically inclined friend to help . Good Luck