Hello Bareftrz, Both distances are 3-1/2" center to center. The holes are 7/16" x 3/4" requiring 3/8" diameter bolts. Half inch diameter bolts are too big for these holes. We recommend galvanized carriage bolts with lock washers and nuts. Thanks for asking!
The leg holder goes on bottom with the slot upward.
Hi Bob, you'll be better off using 2 x 6. Hope this answers your question The Multinautic Team
Hi, yes they do!