Careful with timing
Events and actions a decade or two before can cause outcomes only measurable much later.
For example, I have heard someone comment prior to the collapse of the Bretton Woods System increases in consumer spending correlated to increases in wages. After the collapse of Bretton Woods there is a correlation between increases in consumer spending and increases in consumer debt.
It is highly possible the collapse of the Bretton Woods System in the early 1970s contributed to increasing wealth and income inequality in the late 1980s.
Similarly, the deregulation of transportation and communications in the late 1970s had certain impacts.
The changes to the income tax system were actually fairly small until the late 1980s. It is hard to comprehend how changes in income taxation on the wealthiest have a significant impact in wealth and income inequality, since they only impact one end of the wealth and income spectrum. However, it is possible there is correlation with changes to capital gains taxation and executive compensation.
By far the biggest economic impacts in the 1980s were those due to what John Naisbitt called "Megatrends", and other business futurists predicted. The movement of low skilled industrial labor offshore, the automation of low-skilled white collar work, the decline of skilled blue-collar work, along with the rise in the dual-professional household all had impacts.