looks like the running board will be 3-4 inches lower than the tank in the position its in, so low point may be a relative term
I wouldnt move the running board bracket but I only say that because its just extra work. is there room inboard? where are you putting your gas tank? on my 65 the gas tank was inboard on the left and I could have put a couple air tanks on the right.
I also agree with 99tolife, that a smallish tank will have faster recovery but you will run out of air on about every lift. have you picked compressors? I would consider an engine driven compressor over electric, and with a small tank recovery time is seconds, not minutes. if you are planning on a 5-6 gal tank, get an EDC I guess is the point I am making.
prayers for your wife! I would be lost without mine, so heres to you