4" below your CG or 4" above the bottom of your CC?
The way I decided mine was. First I set where I wanted my lowest CG. Then looked at different options for my throat. Then I made adjustments from there. So I would decide on your throat shape which will determine its height. Then see where that puts you in relation to your CG. And allowing room for your BP. BPs are normally at the top of the throat.
So three things to consider throat height, CG height and where the BP will fit. I've heard the BP can be 2-6"s below the CG. So you have some wiggle room there.
As far as transferring lines. Once you get your throat figured out mark it on the end of your CC. Do you have bell ends or square? I have dealt with the bell ends personally but it's the same approach but I different cut. Pete M has calculators to help.
Good luck!
I used this link for my throat. (I was working with flat ends not bells)
http://www.handymath.com/cgi-bin/arc18.cgi?submit=Entry
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