Log hewing w/ the crown attached

Got a question for those with some knowledges of the school of log hewing. I've tackled one small eastern red cedar and am looking to move up in the world.

Just recently I felled a large ish Red Pine (for non-timber reasons) that has a good section of trunk that would do well with a hewing. I like the idea of hewing with the crown attached for various reasons and my question is as follows.

How do you lay out your beam on the small end of the trunk if there is still a tree attached to it? Do you make an educated guess as to how wide you can make your beam and then measure straight down from a level that rests on the log? Snap the line and hew as usual?

I'm sure I'll have more questions as I progress but that is the one that is catching me immediately.

Thanks!