I will be doing the 500 swap as early as... tomorrow!
I have never messed with one but I know the 4bbls pretty good and it is half of one...
Have you messed with the accelerator pump cam at all? If it is running good with no flat spots maybe you shouldn't!
I really enjoy tuning and experimenting with this stuff. My buddy has a wideband and it is so handy at the point you are at. If I get anywhere with it anytime soon I will share whatever we come up with.
He is so busy it might not happen soon though.