ZFT, the Viscounts operated on the MST-LGW route for Virgin were wet leased from British Air Ferries (BAF) and Euroair.
BAF was a major operator of the Viscounts in the 1980's thru to around 1998 using them in both passenger and freighter roles. They had at least one that had a proper freight door that was marketed as the Freightmaster. For quite a few years in 90's they used them on ParcelForce contracts with 2 based in EDI and 2 based in BFS flying down to CVT each weekday evening and then returning.
I think the Tinnitus I have now is probably down to being too close to too many RR Darts on Viscounts, F27, HS748 and Gulfstream 1 over the years. On the outside the noise was of a pitch that could be quite unpleasant at times, but inside it wasn't too bad on the Viscount.
My first Viscount flight was on a British Eagle VC7, G-ATDR, returning to LHR from LPL. It was filling in for a tech BAC 1-11.
Subsequently I had quite a few flights in Viscounts and always enjoyed the experience