I just got done wiring everything in for my ms and it is not bad. I also didn't have to tap anything. I used 2 tees and moved the stock ats around alittle. I am just waiting on some injectors and will be ready to go. I think you should just buy a set of bigger injectors and go from there. There are people on this board using bigger then 680 injectors that get a good idle and pretty good gas mialage from what I hear. It just seems to be a waste to me to just use ms for supplemental injectors. The only reason you would need 4 more injectors would be if you are running alot of boost. That being said you would need to adjust timing aswell. What are you planning to do about that? The ms can do both with only one set of injectors and give you the same amount of fuel control. Just my 2 cents
sam