As for ignition timing, adjust it a few degrees at a time and see how it reacts.
Porting these heads will give a fair amount of increase, enough to let you cruise 70 into a headwind uphill, who knows. probably not. The intake ports have a restriction next to the valve guide that responds well and the short side radius on both in & ex both have room for improvement.
A good exhaust system with mandrel bends will help the top end as well. I would not go over 2?".

The automatic does eat up some precious power, I spent such a short time with the stock engine and I do not recall the cruise RPM. I do recall wanting the 4.86 gears in mine even with the turbo.