As you calculate the weight, factor in the wt at the highest % sugar you will RO to, not just for 2% sap, Then get a structural engineer to design it.
I've never put a head tank in a loft, but my raised platform for my head tank outside, on my north wall was designed to hold a 415 gal milk tank. It has 4 posts, set 4' deep, on concrete pads , 1 under each leg of the tank, then the floor was just pressure treated 2x4's flat and resting on 4x4 treated lumber spaced 16"O.C.
Don't be penny wise and pound foolish on supporting that much weight. Do it right or your widow could be all alone.
Dave Klish, I recently ordered a 2x6 wood fired evaporator from A&A Sheet Metal which I will be converting to oil fired
Now have solar, 2x6 finish pan, 5 bank 7x7 filter press, large water jacketed bottler, and tankless water heater.
Recently bought another Gingerich RO, this one was a 125, but a second membrane was added thus is a 250, like I had.
After running a 2x3, a 2x6, 3x8 tapping from 79 taps up to 1320 all woodfired, now I'm going to a 2x6 oil fired and a 200-425 taps.