I think you may be right - I took a bad picture of mine last night and I think it says "...at altitudes at or below 4000 feet." I'll have to look again tonight.
In 1977 I don't know if there was an extra high-altitude compensation (HAC) valve, maybe Sascha knows...
"Stay the Trail," "Tread Lightly," and "Leave No Trace" ethics
Rising Sun Bio
2F "Brahma" + Lockright, tach, Warn 8274, FJ60 Power Steering,
soon to lose the Sanden OBA
to go back to factory emissions
Limited TRD 2UZ-FE FOR SALE SOON
Up next: Something that makes a funny whistling noise...