The L175 is 2WD? Started out weighing about 1800 lbs? You are needing steering stability? I'd go for about 200lbs, for no really good reason other than I just put about 260 lbs on my new L3200DT, and that helped a lot! You can click on my name and somehow get to pictures.
What you do depends on how rich and handy you are. Kubota sells a bracket - or sold a bracket to hold suitcase weights, and they sell the weights. You can buy suitcase weights on ebay. If you have a drillpress, welder, and bandsaw you can buy steel, cut it, drill it, and weld it into what I made for my L3200. Or you can build a box and fill it with concrete; This works OK on the back but you generally want higher density weight on the front. Filling the front tires does little good, but filling the rear ones can be a big help. Splitting the brake pedals and using independent braking to assist steering also helps.
