Re-Attach Procedure for Front Brake Calipers

[Wagonpeddler]

I have completed overhauling one front brake calipers for my '81 750C, and working on the other. When I'm ready to fasten them back to the forks, what procedure is recommended? Should I fill the calipers with fluid, then attach the brake hoses, or leave them empty and just bleed new fluid through? Fluid in the reservoir is not new, but not too old either. Should I replace the fluid in the reservoir somehow before attaching the calipers?
Appreciate all the help.
Thanks.