The basic connection at the top is simply a bolted connection. Once you have the bottom connectors engaged, the top should be fairly easy to bolt together. You cannot fix the bolts in place since the top must slide down on the connectors at the bottom.
Another effective way to make the connection is to use two hinge halves which are pinned together with a removable pin once they are in position. The tolerances to allow the pin to slide in will allow this conection to move a little and gradually get looser with wear.
The way I like uses a relatively expensive clamp - Perko flat-mounting hold-down clamp #1112DPCHR. The best price I have found is $29 with most prices found around $45. This clamp locks the two halves together quickly and solidly.