Do you have any idea what caused the valve to fail?

No clue. It's almost like it was defective or weak. I'm sure the solid roller and heavy valve springs weren't gentle on it though.

Have you calculated spring pressure at max lift?

I believe they are at 220# 570#.

Sounds like you did your homework. Whos valves did you use?

They are the Milodon megaflow stainless steel valves.

Ouch! you said it! good thing you didnt try to restart it or have it at high rpms. My grandfathers old 427 dropped a valve and it ended up sending pieces back into the intake and left chunks on the other bank. It ended up needing a sleeve in one of the cylinders and a few pistons and a .030

Well I've got my wishlist all together. I'm keeping the motor all the same with the exception of the solid roller cam and valve springs. I'm going to be losing approx. 80hp with the cam swap, but I should still be over 500hp with the new hydraulic and be much more streetable.

Here's the specs of how it's going back together.

383 stroker / splayed 4 bolt caps

12.5:1 JE forged dome pistons full float
Eagle H beam 4340 rods
GM bowtie iron heads worked over with 2.05 int. 1.60 exh.
Comp cams 12-214-4 Hydraulic cam 305 seat to seat duration .525 lift. 110LC
Comp valve springs
1.6 roller rockers
Super victor single plane intake
Proform 750 double pump carb

I'll update when I get it back in the car. Waving

Do you calculate hp or dyno?

It was calculated with desktop dyno and comp cams camquest dyno. I also had to calculate my dynamic compression and pick a cam that would give me the best dcr for premium pump gas. This setup puts my dcr right around 8.39.