I checked the part books from 1940-1955 they all list 2071209 for the 270 prior to 771209. But the GMC 52 Parts Number Replacements & Supersessions book list the 838774 as the old number and to use 2071209. They used the same push rod 838409. Maybe you can call them and get some measurements.
Interesting....since it subs. to the 2071209 number I'm betting they're functionally the same. If they have a slightly different spec, I would guess the new production 838774's are actually updated to the new spec.
I did read a note in my service bulletins book for the military trucks regarding early style lifters having a small oil hole in the cam bearing face. Later versions eliminated the oil hole and it recommended either replacing the lifters or soldering up the holes during overhaul.
