I can't remember if I asked about this or searched it out, but now I'm even more confused:
How are the cylinders numbered on a 2001 Chevy 3.4 liter (Impala)?
With the upper plenum off, from the front of the car (radiator side) the middle cyl. is stamped as #3 on the intake. When you look at the numbering on the coil pack, #3 is the middle/center on the firewall side......I'm having a serious WTF moment here.  
If that didn't cause enough confusion in my wee little mind, the intake is a cross-ram, and of course the injectors are on a common rail for each bank.  

1     2

3     4

5     6



IIRC

See this is where the confusion lies:
The arrangement "VRMN8R" offers is what the intake maniford offers in the casting, your description is what the coil pack indicates, hence the confusion.

FWIW: Since I had it opened up and we're down a vehicle, I went ahead and installed the injector in the middle cylinder on the radiator side....it'll be a day or two of driving to see if it sets another mis-fire code.....still once it was all back together and I saw the numbering on the coil pack all I could day was SHIT!  

On a tangent: How/what do you use to clean injectors?
I thought about buying an ultrasonic cleaner from Harbor Freight, maybe using it to clean injectors....at $100. a pop it wouldn't take long to offset the cost.

This is because the intake runners criss-cross on their path into the cylinder heads.  So as someone else mentioned, cyls #1, 3, &5 are on the firewall side, and cyls #2, 4, &6 are on the radiator side.

I did notice the runners criss-cross, but thought too much into it: I concure 1-3-5 are on the firewall side, and as usual, if there's a 50/50 chance of getting something wrong, there's a 100% chance I will.  

135 on the firewall side, I have done too many heads on these, i remember it now