If the block is really a 69 it should have threaded lifter oil galley plugs. Those started after 68 and limit the weeping to about nil correctly installed. Also the rear cam plug (besides being installed correctly like LA said) can use a bead of sealer around the outside edge. Also be sure the oil helix grooves -> ////// on the seal surface of the crank are present. If that area of the crank was worn, turned or touched for some odd reason the rear seal will leak. Also be sure the side seals were used installed correctly and tops filled with sealer. Rear main cap gaps sealed as well. Be sure the lip of the seal faces forward and also stagger the seal .250 so they seal gaps don't line up with the maincap gap.

Now... the oil was IN or ON the rear of bellhousing? If on the outside it can be the rear intake or a valve cover leaking. When it drips down can appear to be a rear seal leak.

Are you still selling the car?