It turned out to be a drama over nothing. The noise was actually coming from something catching on a plastic liner. Once I managed to borrow a jack and look underneath it was obvious that the mounts were in fact fine.
I also fitted the polyurethane top bush. It put up a fair fight in situ but I overwhelmed it using a woodworking vice.
The bracket doesn't fit over the bush even when fully pressed in. I had to lift the scuttle tray and undo the bulkhead mount to remove the bracket, then file a small amount off of it.]
I can understand why it may be an acquired taste but I love it. The T5 snarl sounds phenomenal after this upgrade, and yet it is quiet at idle and on the motorway.
It has also solved a lot of handling issues. My engine was evidently shifting its weight about a lot more than designed.