I will definitely consider the triangle plates as my z is higher hence I have the two beams. Mine is higher because I dont want the removable front plate to preposition the spindle all the time when I want to work an a thinner sheet of ice.
I have been thinking of placing one of the rails on the top, but It seems to me that it would be a lot harder to get them parallel, but steel I think that is the right way to go and will do a redesign on that.
Just to give you an idea of what they have got away with on the machine pictured earlier the gantry beam is a 150 x 110 aluminum box section, held by 100 x 50 x 3 aluminum box sections (the vertical bits and bottom bits) and the side plates and z axes plates are 13mm aluminum plates. This hopefully gives you a better idea of what forces are needed for Ice.

Thanks again