I certainly didn't need to lift the body off mine to install the roll bar. It did however, require the application of a little brute force to get all the parts together. All the different angles and joints don't help.
I also fabricated a rear-brace base plate that replicated the original, but in fact, didn't actually do anything structural. It simply bolted to the aluminium boot (trunk) panelling. See photo:
I have some better pictures if they would help.
Paul