putting 89' waggy 44 in the front of my YJ using front springs from the waggy. This is SOA. 44 should have 6 deg positive built in. So is the following thought correct? If the built in SUA perch on the bottom of the housing is set to 0 deg, my caster should be at positive 6 already.

Not necessarily. There's no guarantee those pads were at 0 on that Wag they came from. I would measure the 6 deg at the ball joints.

If you make you perch parallel to the sua perch on the housing you will have the 6 deg of caster that you need.