I had bought a used a 4.11 posi with a ring gear spacer(high school kid did not know anything about those). Jumped on it one day and ripped all the ring gear bolts out! High 12 second 409 stick car 1971. Replaced it with a 4.56 "thick gear" that never missed a beat with lots of 5000 side steps!
No 12 bolts from the factory, but Tom's Differentials and now Strange has conversions($$!). They were a 10 bolt from 63-82 17 spline pinions and side gear/axle stubs for the IRS. So a 30 spline 12 bolt conversion is a good upgrade for high HP motors. Why I as wondering how different the posi is...
Our Impalas etc with a pumpkin take a 17 spline pinion. 63-82 vettes also did. But all the new gear sets for them use a 30 spline -which uses a new yoke. Were the old 17 spline interchangeable with Vette gears?
I have a couple sets of 409 rods and a set of BBC 3/8 rods I'll almost give away! Good BBC rods are pretty decent priced-why pay for new bolts, resizing after new bolts on a 50+ year old 409 rod or even a better stick BBC rod.
Why the Pontiac guys started turning down the rod journal to 2.20 on...
I know lots of the Pontiac guys are using a composite gear(by BOP) or a bronze gear-no melonized made for Pontiac. Lots of guys like the composites but often will break in with a bronze or jeweler's file sharp edges off the cam gear.
There are different quality bronze gears so use a good brand...
Good idea!
On Pontiacs most of the aftermarket splayed caps are 7/16. Factory used 1/2 and many 2 bolt cap blocks are drilled for 4 bolts. I know one guy that cuts off a bolt and uses then on the outer holes he feels gives more support
If doing a HR cam I have stock E head valves and single springs I'll sell you. I went solid roller so higher spring pressure and better valves. FWIW the "standard D port Pontiac" 5.103 valves same stem diameter and exhausts you can turn down to 1.72.
I know some guys say you can run higher CR...