Another update for future LS3 humans that might be reading this:
After messing around with some other aftermarket injectors and questionable data, and not being happy...I decided to try the $55 L96 (12613412).
First drive and all is good so far. Will need to tweak MAF and VVE a tad and then start adding more E to see Inj DC.
I did buy the o-rings* mentioned by Blind Squirrel and they did fit. However, the injectors are taller than the LS3 OEM units and they would not let the fuel rail sit on intake to bolt down. ICT Billet to the rescue with P/N 551307-037. The kit has spacers that are 9mm longer, with longer bolts, and even comes with o-rings. ICT also said to remove the cap at the bottom (see pic) but does not provide any instructions or tips. The ones in the picture do not seem to match mine, and since it appeared to be a single solid piece...I did not feel like chucking up in a lathe and going that route. So I stabbed them in and they seem to go all the way down as expected, so no interference issues with the intake manifold as far as I can tell.
*The ICT Billet o-rings are 3.5mm x 7.5mm ID and these are a MUCH tighter fit than the 3mm x 9.5mm
L96 Shroud to Remove.jpg