I have heard they prefer to have a more straight on flow then the 90 degree, but 90 will work. I would think you would have a more precise control with it on one of the bends.
Thats what I have read too!
Are you venting to atmosphere, or plumbing into down pipe?
What about underneath the crossover, at one of the bends?
I will run a 2" pipe under the right side header and into the downpipe. As far as the bottom bend, That will all be closed in with sheemetal. If I was to install it at the bottom the wastegate would be in the fenderwell in the elements and would be vented to atmosphere thru a lawnmower muffler maybe??