Thanks for this, Brian. I had assumed that the architecture of the TS engine changed when the horizontally-finned head was introduced. I can now see why quite complicated modifications to the ETZ barrel are sometimes recommended rather than a barrel swap.
I shall certainly follow your advice to proceed with caution as I am generally very pleased with the bike as it is and don’t want to spoil it.
Now, I may have got this wrong as well but I understood that the ETZs made for the domestic market were substantially less powerful than the model we are familiar with. Was this achieved with milder porting or simply by a restrictive, I wonder?