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your cruise is probably running on the transition/idle circuit and would be changed by reducing the ifr circuits in your case which would require drilling and installing bleeds if not already installed or purchasing bleeds and redrilling smaller. according to a holley book your idle screws should be out about one turn and the ifr's should be about right. if you're still lean probably enlarge the transition slot, but a little goes a long ways so be careful.

raising and lowering the float level can have a small effect but it is not desireable according to the holley book.

you can enlarge the pvcr to increase your wot a/f ratio but you are pretty close as it is, you will need a set of the small bits which you can purchase at the hardware store and enlarge all pvcr one bit size at a time, these are pretty sensitive also.

if the a/f ratio is pretty steady i would not change the 6.5.

make sure your spark advance is where you want it before you start playing with the a/f ratio as this will have an effect on it also.

the holley carb book is pretty helpful in understanding how they work, and this is what little i understand, somebody else might have more insight and be more correct.

using one cylinder to tune is kind of risky as they all will be slightly different i would bet with off the shelf intake and parts.