Dear Bazlerker,
You have hit the nail on the head. Your Yamaha has umpteen years of technical development over the Vincent yet, if your Vin was converted to the Series D configuration with fully sprung back end incorporating Pettiford sidecar springs , larger section modern tyres, D type longer, and softer but well damped fork springs, coupled with the latest 3" longer saddle the ride comfort is transformed, although probably with rather less performance available than with the Yamaha.
With this set up, solo, my Shadow covered approaching 200,000 miles from 1987 to 2016 without any discomfort.
No longer ridden solo due to a balance problem on my part it has now been converted to what I believe is the only Shadow Trike extant which has had very little use during the current COVID crisis. However roll on next year.