Sad news indeed. I met Peter at Pukekohe in 2007 and he was in poor shape then, having difficulty moving around. I have signed copies of both editions of Peter's book, great reading.
The Greeves Silverstone that I bought from the UK, sight unseen in late 1981, and had shipped out here to Canada to race in our recently organized vintage racing scene, had a heavily modified frame and was fitted with an Oldani front brake. It was only when I came across an article by David Dixon in one of the 1966 UK motorcycle weeklies about the Orpin water-cooled Silverstone, built for the 1966 season, that I discovered that mine was the bike actually modified by Peter Williams when he was working for Greeves, to accept the Orpin w/c cylinder and LE Velocette rad. as well as to alter the footrest position and lower the rear subframe to suit his requirements. He hated the standard Silverstone riding position after riding an Orpin Silverstone in the 1965 MGP.
After Peter crashed the bike heavily at Snetterton late in the 1966 season Orpin removed the cylinder, rad. etc. and these were replaced by a standard air-cooled cylinder in the rebuild. This was the way it was when I bought it and has remained that way since. I have raced the bike here and in the US since 82 and have just pre-entered for the 4 race VRRA series for 2021, Covid-19 permitting. I just love vintage (classic) racing, your bike never becomes obsolete!