1. reduce the longest root back as far as you can to smaller roots closer to the trunk
2. Air layer off the thickest of the two trunks to start inducing taper by pruning back to the thinnest of the two next year.
I think you could probably do both this year if you dig it up and sort out the minimal nebari work in the next few weeks as the buds are popping, then wait til the leaves harden off mid April and air layer.
Your advice is much appreciated - thank you! I was considering doing a trunk-chop right below the two paste-wound areas, but I think I have talked myself out of it.
Will plan to do the work you suggest as soon as I see good bud swell. The tree has some beautiful foliage - will post pics of the work as I am doing it, and once the leaves come in.