Paul,
I'd caution putting the nozzle post-MAF/pre-blade. The reason I say this is once the throttle slams shut at high boost levels and the compressor surge/pressure builds up at the throttle blade you may find that any subsequent alky spraying will get knocked around and end up on the MAFs metering element. Causing MAF hydro-lock.
I am with bruce. Get it on the other side of the blades. Run two smaller fine mist jets. I'd spray from the top down as bruce suggested. However, I would suggest pointing the jets toward the front of the plenum as the flow of boosted air may push the alky to the rear of the cylinders due to the location of the jets. Or you could just drill and tap right behind the throttle blades, spraying straight down and let the air carry the alky where it needs to go.
If you need an extra plenum talk to richie6 he had one that I was going to take for ~$35. I may still have the name of someone with stock TB as well. God I love our GTA community.
Hope I am not talking out of my ass this morning. :???: