Chassis Fixture

[Coyote187]

Hey,
Soon I will be starting to rework and modify my 69, one of the things I'll be doing is changing the multi leaf over to a tri-four bar setup. Now you might be asking why, well I decided on that because it’s just something you don't see every day, also from what I've read it is a very lets say tunable setup. I have never done anything like this before, but I am a welder/metal fabricator and have been for the last eleven years and I have a good Idea on what I can do.
Now my question is when I build my chassis fixture, what should the mounting points be and what dimensions do I need to concern myself with? I understand that the frame rails have got to be square and the placement of the rear-end is very important. But does the body need support any where in particular?
If anyone has drawings or pictures that would be a big help.