Injectors have come along way since the typical "Sard/Nismo/Rochester" injectors came about. I'm running ID2000's and they idle and drive better than my Sard 800's could ever dream of doing.
Buy the ID's and put them in. You won't regret it!!'
I can't see the intake manifold being the best place for that sensor (WTF were Nissan thinking?).
Anywhere between the cold side of the cooler (where you have circled) and before it hits the engine bay. That way it doesn't get warm from heatsoak.
Thats a decent idea but the 'balance tube' has so many nooks and crannies that it would take a month of Sunday's.
I went down and bought some degreaser and a wire brush. Came up well.... Now its in the dish washer