Checked the compressor was outputting OK, got it all installed again, with some tap washers under the lower mounting washers as spacers / absorption to see how the noise is. All connected up, fired straight up happily, had to run for 5 minutes but then came up to access OK. Didn't test higher, will wait 'til actually driving. Nanocom cleared the compressor fault message and got it going fine. Quieter than it was, more of a bass throb like a big exhaust instead of a rough harsh noise. Still scope for improvement.
Got the 20" wheels photographed for sale - don't want to be dragging them with us when we move. Posting that in the sale bit later, then eBay next weekend.