Got both sides welded up. Ground out the area that looked liked it cracked on the first manifold. Not sure it was actually cracked once I ground it all back. Used the oven this time and preheated the manifolds to 450. Welded it up, then put it right back in the oven. Slowly lowered the heat over the next few hours. I used my infrared thermometer to make sure each side (cast vs stainless) was at the same temp before lowing the oven by 75 degrees each time. I looked them over this morning before work and didn't see any cracking.
Ordered a VS Racing 44mm wastegate, bellow, and a schedule 10 2'' to 1.5'' reducer to mount it with.