pushrods came off

Looking for some help, we have a 526 new century big chief heads t&d rockers, med sized cam not over .800 lift we ran the motor first weekend no issues went out 2nd time and first pass pushrods on #7 & #8 cylinders came off at 4.1 seconds into the run,and we can not find any reason for it other than the exhaust valve on #7 looks like it tried to pull the keepers through the retainer, none of the pushrods were worn or bent the lifters are fine the spring pressures are good all the stands are tight. all the adjusters were tight, any thoughts would be appreciated,

 

We ran a combo like that for years and had some weird exhaust carnage until we had the cam reground with slower valve action on the exhaust.
We ran huge heavy pushrods and pretty good components throughout. Never had any issues up to 9000 rpm and 46 psi with screw.

 

Update, found the problem although spring pressures appeared to be ok on the head once we pulled them they were shot, we tried a comp cam spring they had 5 passes on them since new and never saw over 8800 rpm and they are junk.

 

Pac 1360. Can't go wrong. Last forever at that rpm. My Chevy had 950 lift and those springs would go 50+ runs never losing psi.

 

Did you hit the limiter? Seems everytime we hit the limiter, we have a few junk springs. Out of curiosity what lifter are you running?

 

No where close to the rev limiter,