10.5:1 Pistons for '66 273 Block w/ '67 920 Heads

The 920 heads (66 and 67 273) are the same as the 178 (early 66) and 234 (late 66) heads. I never have found out why the number change between the heads. They all have the same valve size and rocker design. A slight difference in ports could be the difference. My 273 had a (if I remember correctly) 178 head and a 920 head. There also was a newer rod bearing on one cylinder. I imagine something broke and a rod bearing and head had to be replaced.