Less than 1/4" on the steering wheel with someone holding onto one wheel. That's pretty tight though and 1/2" I would accept as good.
Greasing as you clearly know is the big one to do regularly, the spanner tightening becomes more important if you have rougher roads as the chassis has to work harder if that makes sense.
At the moment our local councils are short of money so we end up with +1" potholes in a lot of our roads and the Morgan suspension crashes around into them and generally loosens things up at the front end.
Unrelated to the wheel balance but a good check to do annually is to tighten up the "U" shackles holding the leaf springs on the back axle.
Glad you are enjoying the big 8, they are a very special car to drive I find too.
