Tilton and Wilwood and Coleman machine all make master cylinders that have interchangeble reservoirs that are shorter than the one you have on your firewall. There are remote reservoirs available for those as well.
Like F&J said, you don't need much fluid.
Here is a pic of a setup I'm working on right now, a 65 mustang with hydroboost and hydraulic clutch. I'll take some better pics of the available adapters and stuff that came with the MC kit so you can get an idea..
Just out of curiosity, how does that clutch setup feel as you have it installed? It looks like it might be stiff.
my signature lines...not really directed at anyone in particular..
BE different....ACT normal.
No one is completely useless..They can always be used as a bad example