My 53 KK I had no breathing problems not running a generator. It did not dump oil out the breather tube. It also had -52 R heads on it . I had my 55 KHK engine on the bench at the same time as the 53 KK, all measurements on the heads were the same, depth was the same on either head for the 53 1,2,3,4 cams and also on the KHK heads for the 1KHK,2KHK,3KHK,4KHK cams.
Some pics of the speedo drive that was recently on ebay. Note that this is a Corbin, not a Smiths as in my previous picture. Emailing someone whose knowledge I respect, it was concluded that the Corbin would likely be the manufacturer, as we couldn't see Brit parts being used.