Well you kind of left out a some things draft, weight, would be the most important,
The yacht club I used to belong to had all the boats on trailers usually builby the owners and basically cradles sitting on wheels or flatbed trailers modified so the cradle could sit on top, in just about every design we used a "cow chute" to guide the keel to the center,
what you may want to do is take measurements using the bottom of your Keel as the Baseline and then measure out to where the stands are presently (if they have it on stands) make uprights for the screw adjustable pads or in some cases people just weld it the jack stands to the cradle or trailer
another words guide words that would guide the kill to the center of the Cradle or trailer it worked pretty well
This was a yard trailer cradle I called it a wheeled cradle we used Ford twin I-beams for the axles the cattle chute guide board was been removed for bottom painting