bent pushrods on initial run in?

[crossy]

Alright a few weeks ago i posted a question asking what would be the length of pushrod i needed for a 1990 block with earlier heads. the heads are #882 which are the better 'bad' heads from the late 70's. Very professionally done, all new valves & such. There should be no isssue here at all. this was NOT a roller motor so the stock 7.800 pushrods are the right ones? I ordered up a set of no-name hardened pushrods because these heads do have Z28 springs,guide plates and screw in studs now. Anyway i know what I'm doing when it comes to adjusting hydraulic lifters. i do one cyl at a time. done it my way 50 times before and never an issue. never have to re-adjust either. I had the intake off when I did them and verified my work. So anyway, I'm almost always there when something i built gets fired up. I wasn't there for the first 5 minutes. They said they had it at a high idle, like i told them to do, and that it ran fine, but yet they were installing a new carb when I got there because they said it blew back up thru the carb(eddy 600). I found the timing to be very retarded and when I fired it up it was 'ticking' exhaust back thru the carb. i knew that was valve adjustment type issue. when i pulled the left valve cover- ALL the exhaust pushrods were bent bad. The intakes were fine and the whole other side of engine is fine. They said when they shut it down it 'popped'. I measured these new pushrods and they are 7.800. My question is could the timing being that retarded cause these cheap (hardened) pushrods to bend. thanx, crossy

1990 350 TBI block
1978 350 #882 heads
cam is hyd and only .460 lift