You can still set it by ear. Race guys do that at the track and it can be helpful when making your own custom chips. But the computer covers such a wide range compared to an old distributor that it's easy to get it right in one place and wrong in a bunch of others.

I'd leave the timing wire connected. The idea is to see if a little more or a little less timing at idle helps.

Most of the chips are made for a stock engine. I might be able to find an older one with more spark advance but if your truck still has an old one there's not much to be gained in the swap.

Keep us posted.