IIRC, SP 423 pistons are a 4 valve relief, round dish piston. If that's the case, even w/an ideal quench distance, the quench is compromised by the round dish.
The 1.54" CH rebuilder specials w/a minimal 0.005" cut to the decks (for shim gaskets to seal), still will have a quench of ~0.055" (~9.020" deck height + 0.020 shorter piston compression height + 0.015 HG thickness). Or you can go ahead and cut the deck 0.020"- at more cost for the machine shop labor, plus less strength to the decks- to get a 0.040" quench figure.
Or bite the bullet and buy pistons that have an inverted dome and a CH of 1.56". Give the decks a skim for steel shim HG seal (keeping as much deck thickness as possible), and get a better quench from the D-shaped dish along w/a tight, 0.040" quench distance.