Pushrods, how do I measure for...

I originally voice commanded out this long post on how pushrods work ect...
but I scratched that as the world is full people with $$ and bad mechanic's to take it.
IF you brought your car into a mechanic because it was not running right and the mechanic told you it needs new pushrods because they got loose and that was it? then likely you've been taken to the cleaners.
I've kept in mind that I'm just an internet dumbass and your mechanic is someone you shake hands with that look in the eye but I understand that, But facts are facts.....