How tall are your jack stands? I've always used the "5 ton" capacity ones that have a fully extended height of around 2 feet. If more height is needed for some reason, I usually use pieces of 2X8 or 2X10 lumber cut into lengths big enough to span beyond the stand base legs by a few inches and place two of them side by side to give a solid base for the stand. Stack up a couple of layers or more if necessary. If the surface you're working on is gravel or grass instead of concrete, having that steady base is really important. When I was working on Ed Pruss' big GMC 530 which was too big to fit into my shop comfortably, I fabricated stand bases like that and even assembled them permanently with screws and 2X4 cross braces. They have come in handy several times since then.
Jerry
