Oil Change Interval for the Slant

My daily driver has been in continuous use since 1964 (bought from original family)
Original 170, well over a million miles on it.
I put 30,000+ miles on in a year.
Had it 4 years..120,000 miles. One oil change in all that time. No leaks, no smoke, six good cylinders.
Waiting for it to die so I can drop in a 225. Dont look like that's gonna happen anytime soon