I've decided to take Romans advice concerning the dynamics of these engines & how they work up top & not so much down low so, in order to take advantage of their inherent performance characteristics, I've decided to swap turbine housings. I will run with the .84. & not the .63. I may as well swap it now while it's sitting on bench than later after it's fitted to the car.
I don't want the back pressure & accompanying heat on the turbine wheel & inlet parts that the smaller housing would create. Besides. The better economy & higher hp I think kinda speaks for itself
Just so happens workshop has an .84 housing from a commodore they worked on so it isn't a big deal.