Help with Backfire

Check your rockers and pushrods. Not uncommon to poke a pushrod thru a stamped rocker, or bend a pushrod.
Especially if you did any spirited driving, and/or missed a shift.
Nope, this time you won. I'm experienced, lol, used to carry a coupla spare rockers in the glove box, right beside the spare ballast resistor. cheers.
Well, now I've got a new problem. I got a new set of rockers at the junkyard, pull the old ones off, and the exhaust valve right next to it is broken off. half the stem is still in the retainer, and the other is in the head. I tried moving it and it is real right. The machine shop just went through these, so I'm not sure what the issue is, but there has to be something. I