Nice Chevy II! As he stated the main thing is to upgrade the suspension, brakes and 5 lug. You do not NEED to use Mustang II kits. They have the Mini Subframe kit from CPP that has different kits you can buy. They have a basic, middle and higher end. Basic I think has just lower control arms, springs, sway bar, mount brackets, etc and then the other higher end kit has upper and lower control arms and a few other things. They also have a complete disk brake 5 lug upgrade kit with power brakes. As for power steering, I have the stock steering wheel on my wagon with the 327 and it turns easy with manual steering.
If you have the money then you can go with the Fat Man kit and like he said it will shave a little weight off and be all newer type suspension that should handle much better. These cars with stock suspension and sway bars still handle great though. It all depends on your budget.