Which engine do you have 396-cid 425-hp with 11.0:1 compression ratio? or the 396 375 hp?, 396 325 HP? etc, piston ranges were from 9:1 to 11:1 forged! What pistons do you have?
four-bolt main caps?
The 1965 396/425 HP,
The 396 was offered in several configurations and produced different horsepower and torque ratings, depending on its intended application.
The 396 with a 10.25 compression ratio produced 325 horsepower at 4,800 rpm and 410 ft. lbs. of torque at 3,200 rpm.
The Z16 performance 396 with a 11.00 compression ratio produced 375 horsepower at 6,500 rpm and 420 ft. lbs. of torque at 3,600 rpm.
The 396 with a 11.00 compression ratio produced 360 horsepower at 5,200 rpm and 420 ft. lbs. of torque at 3,600 rpm.
And the 425 hp version that produced well over the rated HP
A Side Note:
The correct cam bearings for the engine you have is very impotent some take a grooved rear cam bearing #396 Clevite SH615S 65-66 only!!!
Clevite SH616S 67-93 396-427.