If the stock wastegate is not adjustable then that’s what it is. I’m positive it was never changed out. No boost controller either.Post a picture of your wastegate arm.
What I do is roll until I hit 3rd gear & then go to WOT. With my boost gauge I can see where it’s maxing out at & make adjustments up or down from there.
Again, patience. At a minimum get your Hotwire & fuel pump installed. Then adjust your fuel pressure(vacuum line off). Then you can start seeing where you’re boost is.
You don’t want to blow any head gaskets over an easy job.