I have used a Forstner bit in a drill press on aluminum before - wasn't what it was designed for and it will probably make the real machinists cringe, but it worked for me. It churns out tons of very thin, foil-like swarf that you have to clear regularly, and it goes really slow and things heat up fast. I kept a spray can of WD-40 handy and tried to keep it lubricated, and I had to pause several times to keep it from getting too hot.
I'll bet if you drilled the 13/16 hole with a regular drill to remove the bulk of the material, then finished with the Forstner to just flatten the bottom, it would cut out a lot of the work.
Found a 13/16" bit here for $5.99:
http://shop.woodcraft.com/Woodcraft/...=false&GiftID=