Yes, maybe not recommend on newer engines.
I imagine the old sixes have simpler maybe larger oil passages with less chance of getting clogged when flushing.
Please don't take my suggestion as experienced recommendation - every old engine is different and unique with sludge build-up of course.
I would take off all the covers and do a thorough visual check using common sense and good judgment.
If the sludge build up is not too bad and you feel confident, use maybe more than one good thorough flush, after you removed as much by hand as possible, where accessible.
It might reveal other problems, but better than driving around with a mystery to be revealed at typically the worst point in time, when you least want to deal with it.
