I don't recommend converting shaft heads over to Jesel heads because you have to redrill existing holes. If you have the choice it would be better to start with new heads that are machined up front for the Jesel rocker arms. That isn't always an option but it would be the recommended way to go.

I re-drilled my EZ heads for the Jesel conversion and it came out okay but I have access to better equipment than most people. I had to engineer my own setup because Indy wouldn't provide a Jesel setup for the EZ heads. If you're starting with 440-1 heads then at least there is an off the shelf rocker arm kit for that head.