How much "shake" at idle is acceptable?

It runs fine above 1000 rpm all the time. Maybe this engine just doesn't like to idle at 900 rpm

Easiest thing you can do and probably the cheapest is throw a set of plugs in it.... If you have removed a vacuum leak from the list then timing. The video you posted with the Auto tranny is definitely a smooth running engine and the AFR on your interface is showing it's fat but it should have been in Open loop....

JW