I can't believe that there hasn't been a jig made up for headers yet. I have a set of twin headers ( non ATR's ) that I plan to have the collector flange cut off and v bands attached to . I feel that it gives me the most amount of mounting options. I believe if the headers are made to that point the hard part is over, then people can design around water and oil pumps , alt mounts, etc.....
NO WAY!
I would like to share my limited experience. However, it does not apply to a single turbo application. But this shouldn't matter much though. It should work for you as well.
Forget the headers for now!
If you think it's better to have the headers built first,
I promise you, It's headers that are the easy part!!!! Not the rest!!! The headers are just one thing and they have no external moving parts or lines to get pinched or wires and hoses to get burned or pulleys that need to be aligned.
First drop in the motor. Mock-up and put together your entire set-up. Pulleys, water-pump, fuel system....everything.
THEN, mount your turbocharger w
here you want it by building a permanent bracket or stand that securely fits it within your set-up. Of course, while doing this you should somewhat consider the necessary required real estate needed for the headers. But leave the details for later. Then when all is done, you can build (or have the headers built) to connect the dots.
You build pipes into a house. You don't build a house around pipes! Same concept. Kinda.
Do not let the headers dictate your turbo location. Do not be forced to build headers that need to support the weight of a 35 lb turbo when they are 1600 degrees. When complete, you should be able to remove the headers with the turbo in place. Do not get caught having to come up with ways to work around someone else's idea. Don't worry about giving yourself different mounting options with slip connections or v-bands. You won't need them. You will have everything right the first time. You won't kill yourself thinking about all the little things that just don't fit right.
If the header builder is competent, let him work it out. I'm not that bright. I never built a set of headers before in my life and I was still able to do it this way with very little issues to work out later. Biggest problems I've had in about 10 years was a few heat shields and aluminized wire loom requirements in a few areas.