I have plenty of RPM, so that wasn't my problem. Anyhoo, I ended up just doing as the manual said and inserted the manifold all the way into the pipe after cutting about 1/4" off. It ran it fine last night with no glitching what so ever and PLENTY of low end power now. It really is amazing how much of a difference it makes vs the stock manifold. I think I'll try porting the manifold as soon as I can get my hands on a dremel.
I was thinking about doing some sleeve modding, but I'm a little afraid to do anything to this engine. It's already ballistically fast, and now with the cut manifold, it almost perfect. I'll probably stray away from hacking away at the sleeve for now, and just wait till the motor is scrap and then try playing with it. I'll just get that CrazyNut Racing head and just leave the car be from then on.