First, I hope you don't plan on doing 128mph on the street. I also hope that when you do actually try to reach the vehicles top speed, you do so with the right tires. Not all are created equal.
Second, with the right tires and the speed limiter removed, I see no reason why that vehicle couldn't hit that speed in stock form. Might be a good idea to install a driveshaft loop as cheap security.
As far as the modifications you have planned, I don't think they're going to net you much in the horsepower department. Perhaps DoubleVision will see this post and comment, he seems to know quite a bit about making power with 4.3L's. I've heard it takes deep pockets to make one move.