Bowing to peer pressure A body style

So junction City Oregon function for junction last weekend. A really fun event over 600 cars Good times over a thousand if you count the cruises. So during the all years cruise on Friday night one part of the route people were burning off big time a lot of late model smoking up the horizon and the crowd was loving it! I rolled up with my 340 pack and staged with style, I run drag radials so I knew I had that hit it hard to break them loose 45,000 RPM launch and laid it down in classic 340 style. But on the way home I felt a small vibration, I never ignore vibration after jacking the car up the next day I seem to have excessive lash in the rear end. My question is is there a way to check lash in a assembled drivetrain or how would you determine to much lash.? What's the magic number on a 741
45,000 rpm - nice!
It must have a Full Race cam. LOL