Instead of screws and nylocs, you could have used pop rivets, which protrude less from the installation.

Andrew is going to be posting info on how we did this for a ZX install recently, in almost the same manner you describe. This does give a very rigid structure to the cage, and is semi-permanent: however, the rivets are Aluminium and can easily be drilled out later if neccessary.

One of the few remaining Mk1 owners... #00015