OK so we've come up with a build plan.
Block was not align honed for use with main studs previously, which caused badly uneven bearing wear. This had nothing to do with why the valve and cam broke, but a definite problem that needs to be corrected nonetheless. Block will be getting align hone for studs as part of the machining process.
0.060" overbore, making the motor a 468.
Going 9.5:1 compression (like before). Stock GM crank and rods. We'll be using a race bearing this time (originally used Clevite77 bearings) upon recommendation from the machinist.
Pistons are made by Probe Industries. Supposed to be stronger than most available and they're made in California.
Cam will be SLIGHTLY hotter than what I had before. The last cam I had was a single pattern cam...going dual pattern this time. Here are the cam specs for the old and new cam:
Old Cam: Isky 280H Mega
110 intake centerline (installed at 106*)
60* seat-seat overlap/12* 0.050" overlap
New Cam: Comp Cams XM278H
Intake Lift: 0.564"
Exhaust Lift: 0.566"
278* intake duration/292* exhaust duration @ 0.006"
234* intake duration/244* exhaust duration @ 0.050"
110 intake centerline
61* overlap @ 0.006"
Both heads are getting replaced. GM OEM casting 353049 large oval port with larger valves (2.190" intake/1.880" exhaust). 1-piece Ferrea stainless valves. Hardened exhaust seats.
Same carb and intake as before...Holley Marine 750DP and Edelbrock RPM Air Gap manifold.
With any luck I'll end up with the same top RPM as I had before. I'm only changing the shaft seal in the pump but all the internals...impeller cut/clearances will remain the same until I know where I'm at with the new motor.
More details to follow as the build progresses. Due to financial limitations it's lookin' like I won't be able to start reassembly until late January.