Keep your eye on eBay for people selling off parts from estates and such. As for ABC piston and liners, maybe Brian Gardner could do a run but he's usually pretty well backed up with projects. For stuffer back plates, they have been made by several people including the factory.  Marvin Denny did the first ones along with the hemi head. If you just use a standard, stock back plate with a thinner gasket or no gasket and some sealer, you will achieve about the same thing Try taking some depth measurements and see what you get. If you had a piece of the proper material, I think you could attach a pad to the face of the back plate to fill the gap and leave just enough clearance for running. Attach it with some JB-weld and a rivet right in the center so the crank pin rotates around it.  Stuffing the backplate in itself doesn't do much of anything noticeable, but combined with some other detail work, can add to the mix.
  Type at you later and HAPPY NEW YEAR!!
     Dan McEntee