Mine did that in 1972 or so because of the shock mount loosening up
(original style, not the later style with the kit). I had a friend
who was an aircraft welder who welded it up for me and 30 years later
it is still fine. The important thing is to keep everything there
good and tight so it doesn't hammer. Rear suspension noise = cause for
concern.

By "valve jobs" I assume that you mean you take the head to the machine
shop and they do the job and you pick it up and put it back on.
Should be less than $150 for a 6 cylinder engine in this part of the country.
Urban or coastal areas probably more.
--
George Downs, The "original" Walrus3, Bartlesville, Oklahoma