exhaust idea

I am going to redo my exhaust on my 87 Turbowagon and I came across something interesting. The exhaust port on the heads measures roughly 2 inches in diameter. The exhaust pipe is large in outside diameter but the walls are very thick and the inside diameter is only about 1.25-1.5 inches. Could I bore this out to get better flow or would it hurt the turbo?

I also want to keep the existing downpipe but want to modify it. The flange bolting to the turbo is a horrible design. I was thinking maybe a second pipe could be welded on so the wastegate exhaust could be separated from the rest and introduced further down the exhuast. Much like some WRX downpipes. I just wanted to know if anyone had messed with the downpipe. Also I wanted to know how hard it would be to cut the cat in the downpipe and replace it with straight pipe.

I think i have way too much time on my hands but i was wondering if these mods would work. thanks