I think I am missing something here. Are you talking about getting a crate engine and then adding the supercharger to that?
If so I think you will basically be in the same place you are now, unless you are going to have an engine built to take advantage of the blower you will be in the same boat.
By skipping or holding off on the fuel injection that can save you a few bucks and make things a little more simple. Once that is sorted out you could always add fuel injection later.
If you/he wants a blown engine the basic rules are (if he wants to make power), forged pistons, good rod/s bolts, forged crank, and low compression 9:1 or less. If you have those basic things then typically you can bolt a blower on and make decent power.
If you are looking at a GM crate engine I don't know of one that fits that description, there may be one I just don't know what all they have to offer these days.
There are a couple places that offer ready built blown engines Bad ***** Racing Engines (Sonoma, Ca) and Speedomotive (Southern Cal)are two that come to mind.
I am not sure what you are thinking at this point?