Edelbrock Victor small block head……

T. Fritz said

I currently have center/standard lifter seats, haven't had much luck finding offset ones. I am running hydraulic roller lifters. Yes I am using the Hughes roller rocker set and have verified the correct rockers are in the correct locations. I don't know the spring loads. Cam is a Thumper with .513int/.498exh lift. Pushrods are 5/16 diameter, I don't know the wall thickness off the top of my head.

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Couple more thoughts:

Since it happened on the same cylinder, maybe too much preload on the adjusters? Or not enough?

Or, have you checked retainer to valve guide clearance? Or the shim packs under these springs, may be binding the coils if something is set up different on #5.

Not being a jerk, have you floated the valves?

Also, did you have the heads checked out by a machine shop? I had some guides that were tight, although this may burn the valve first.

Just throwing more stuff out.