The dampers really don't increase the rate much. Those are the same springs used on my comp hydraulic roller. They aren't that stiff. They probably didn't A: use break in oil with zinc. B: didn't keep the RPM up or varied it.
Ok, let's go with the theory that the double springs aren't the cause of the bent pushrods.
If so, the next thing down the line would be the mushroomed lifters binding in the block - but if that were the case, wouldn't we have seen at least four valves smacked at cylinders #2, #3 and #7? At worst, we have two valves bent at cylinders #5 and 6, and zero indication of them having smacked the pistons.
It just doesn't make sense, and that's what bothers me. I am not going to start throwing parts at it until I know what caused the stock pushrods to fail - because they didn't fail on their own.
Furthermore, the break-in procedure is pretty much a case of the darn engine starting up right the first time - and to continue to do so for 30 minutes. No workie, cam wipey.
Funny thing, I learned this evening that at least one of the cams that came with the 400 (dare say not the '77+?) cam isn't that far from the 351C 4V:
351C 4V:
Lobe lift: Int 0.247 / Exh 0.262 /// Theoretical lift: Int. 0.427 / Exh 0.453
400 2V:
Lobe lift: Int 0.247 / Exh 0.250 /// Theoretical lift: Int. 0.427 / Exh 0.433
This will sound stupid, but I know I can dig up more than one 400 with matching lifters at the junkyard. Question is - truck cam or not? Who knows? Too many variables to be feasible.
Nah.
-Kurt
P.S.: On that note, it remains to be seen whether the lifters scored the block to the point of sleeving.