Personally, I wouldn't be comfortable either, what sort of weights are we talking and how do you know what the load bearing capabilities of the wood is, I used to work in the steel industry and the strength of steel can be worked out - I would be suprised if wood was the same. If the adjustments are small, could steel plate type shims be used?

The load bearing capacity of wood varies, both with wood type and with the direction of loading, but it can be assessed. I don't understand what you mean by a narrower centre of gravity - please explain. While knowing the load is good, you also need to know the cross sectional area over which it will be applied, so that you an work out the stress. As for displacing the wood - a legitimate concern, there are ways in which you can lock the wood relative to the legs. Alternatively, the wooden packing pieces could be made significantly larger than the feet of the platform.