got the blower working in his gen2 motor swapped, gen1 LS. Search his name, he gives great pictures and info, albeit somewhat incomplete he has shown its possible to get the blower on the motor, among other things. (used a mustang v6 manual trans to convert his LS to manual too)
Sounds like the OP has a gen1. I would try to find a pull-out from an STR and just get that stuff to work in the LS, then use all the resources/knowledge and CNC learnings to maximize that powerplant vs trying to adapt the gen1 3.9 to take on a supechager and factor in all the "math" of adding boost to it. Both are challenging paths no matter what. But the 4.2 starting point seems safer/better.
Either way good luck and document your progress. While I'd like to take HRLNKN's bet, I have more to gain from seeing this pan out than predicting its unsuccess, haha.