I agree with the others on the support. before you set weight on the supports add a piece of 4 x 6 between the three laminated 2 x's and the support, use simpson HD 2.7 to connect the 4 x 6 to the three 2 x's, at the bottom add a 1/4" steel plate with holes cut in each corner or at least on two sides and anchor with 3/4 swedge's (do not drill through the bottom of slab and if you do drill over size and put althreat in with simpson epoxy. This will give you a great load distribution, relieve the point load a bit on the sq. thin plate at top and bottom of jack. just a thought for you to consider. You can brace with a 2 x 4 now while you make the modification and I do believe you will in great shape for the long term. good luck keep us posted. looks like a fantastic project to follow and I am looking for the build out of your system. :whstlr: