Jerry & Harrell,
IF the engine had been previously bored out to accomodate the 235 pistons, maybe they machined it for insert rod bearings at that time? Seems feasible, since I just had it done to my 216, and I don't think it's exactly a "new" trick . . .
Harrell,
If I recall the specs right, I think the Horse Power difference was 3 to 4 between the 216 & the similar 235, but the 235 had a greater increase in torque . . . not sure what this helps, just thought I'd throw it up the flag pole and see who salutes . . .
-Michael