Dick Lang did not race 1965-1967 due to a dispute with the IRS over the status and purpose of his racing. When he prevailed in the dispute, he returned to racing in 1968.
For those of you into tax cases, you can read it by clicking on the links below. This case was also important to car dealers as it upheld the use of "demo" cars by family members of dealers.
Tax Case Page 1
Tax Case Page 2
Tax Case Page 3
Tax Case Page 4
Tax Case Page 5
Here is 1968 article from the Dayton Daily News (click to read):