I have the '82 shocks and when there is no air in them the bike bottoms out ALL THE TIME!!! Gotta at least have 28 lbs but I find 42 lbs works best.
If you are looking to flatfoot it, than I suggest you try what I did. I lowered my triple tree 1 1/2" on the front shocks which now allows me to come very near flatfooting the ground! It actually helped my handling at slow speed too!