I wouldn't worry about 1/2". For years the front LHS of my 1958 TR3A kept getting lower and lower and no VTR or TRA judge ever noticed. Either there were different judges looking at the different sides or a judge forgets it looked sagging when he goes around to look at the other side. Long grass helps to hide this too. If you really want to fix it, you could loosen the inverted "U" bolts holding the spring assemblies to the axle and add a block of steel or aluminium to "shim" the sagging side up.