you seem to have missed the point, same casting would do a 9 or 10 stud barrel just drilling as necessary.
If their is any other difference its probably internal.
Never heard of this Palmer bloke, lots of Triumph 'experts' out there, one or two may even have been born before Triumph went bust.
Me, I have owned ridden and worked on Triumphs since 1965, seen most of the bodges but there is always more.
Some pictures would be a great help, does it have push in or stub fit at the head?
Send pics of the muck oozing out the gaskets for a gloomy assessment.