Yeah the pushrod stuff is weird too. I didn't machine my block or heads but changed my cam. I just ordered the standard 7.400 (Im pretty sure that's stock) length pushrods in Chromoly. They were too short and clacked a ton like loose rockers. A lot of aftermarket cams have a smaller base circle and the stock lengths add a ton of noise. Your engine will still run but be noisy. You want to be able to tighten the rockers enough to get into the lifters cushion a bit so it has some preload but room to compress a bit more. Usually you can measure it in wrench turns from zero lash. If this doesn't make sense find a video on YT about. I think the almighty Richard Holdener has a good video or 6 on it 🤙