Were the clearanes on the Donor XL7 this tight also 
This looks like a factory install.
You totally transplanted that V6 manifolds and all, good work 
I didn't have the whole car with the motor but i have looked at a few xl7's and they have alot more room under the hood,especially in front by the radiator. I actually had the stock belt driven fan crammed in there at one time and when i stood on it one day the fan hit the radiator and tore it up! So i had to go to my original idea and use electric fans....and a new radiator.

You have no choice but to use the stock exhaust manifolds which have the cats welded to them with a oxygen sensor before and after the cat on both sides(4 oxygen sensors). Stu.