Lee, I have the same setup and it is a real pain!  The header tank has to
come off.  Last year I was able to prop the canopy open with 2X4's (so I did
not have to remove it) disconnect all the fuel and electrical lines from the
tank and get it off.  It is tough to get at, for example, the sump drain AN
fitting under the tank but doable if you doublejoint one forearm and extend
the length of a couple of fingers on that hand.  Maybe there is a better
way. 

I found it useful to use teflon/ss braid flexible lines for the header tank - this allows the deck to be lifted from one side and both arms can get at the underneath connections - especially if the sump line actually comes out to a human reachable union.

 

<<<<<Once you get at the master cylinders it takes a syringe to get fluid
in there and a dip check SWAG to check the level.  I suppose it is possible
to thread something in the little filler holes and run Nylaflow tubing up to
a place under the instrument panel cover.  Let me know if you develope a
fix.
>>>>>>

 

When I had the original Matco master cylinders, one could reach them by removing the canopy and the instrument panel dust cover and reaching between the tank and the panel instruments.  One method is to wrap the masters with a towel and pump fluid into the brake body until the fluid runs out the breather hole in the master - then drain a small amount of fluid out of the system.  I finally gave up and installed the larger Matco brake cylinder that requires a remote reservoir.  I used the Matco clear plastic one mounted to the aft side of the firewall and, once half filled with red mil-spec fluid, just a flashlight illuminated glance into the foot well tells me if the reservoir is at the proper level.