I got the exhaust essentially done this evening. It was done a week ago, but the v-band flanges warped from welding and were leaking. They are the lipped stainless flanges, so sanding them flat would be a lot of work and not guarantee anything. Instead I made some small gaskets out of desoldering wick (woven copper ribbon) and coated them with high-temp RTV. Seems to have done the job.
I had to use the actuator from a Chinese ebay turbo that the wastegate assembly came from because the flapper post is bigger than the stock one. I could tell it has a stiffer spring and after setting it up with stock preload, it makes 15psi on the gate alone. That's alright, but I'd prefer having the 10psi option and will have to make a new end that fits the old actuator threads and the new flapper.