The 383 stroke is just 1/16" longer than a 340. That's what saves it. at 6500rpm the max acceleration is 2560 Gs. So the piston and the top of the rod "weigh" less than 10,000 lb at the top of the exhaust stroke. The 3/8" rod bolts can handle this.

If they haven't been torqued properly or have some sort of material defect the rod bolts can stretch enough to lose clamping force and allow the bearing to spin.

It can all be calculated.

R.