Does any know if it is legal to put an air tank down stream of the pressure regulator in the 60 psi section of pneumatics?
Yes this is legal.
Figures 4-16 and 4-17 (R85 and R86) show air tanks on the low pressure side of the regulator. While no diagrams or rules show it, I do not see anything that says you can only do one or the other.
It is fine. Do you need a large amount of air in a short period of time? Too much for the regulator to pass in that short a time? That’s the only reason I can think of to put tanks on the low pressure side.
Off course there is no rule about what size regulator you use. 
My evil twin wants to use a 1 in one just to harass the inspectors. My good twin says it is never a good idea to do something just to harass the inspectors.
Especially when those inspectors read posts on CD, will be at your event, and inspecting your robot… 
Fortunately for my team, the inspectors know me and make allowances. I think they feel sorry for the flying monkeys. Oops I meant to say the youth. I am not supposed to can them flying monkeys any more. :eek:
Are you sure??? I think I need to make a trip and make some surprise inspections.
Always happy to have the company. I will try to make sure my evil twin is taking his medications.