If I recall correctly (and we're talking old, old memories here), all the early 727s had the oval center inlet (both -100 and -200). At some point Boeing introduced the 727 Advanced with several updates - one of which was the round center inlet.
Originally Posted by
WHBM
I wonder if any of the original 727 tooling is still in use at Renton on the Max.
Probably not in Renton - the 737 fuselage is made in Wichita (by what is now Spirit). But I'd bet some of that fuselage tooling dates back to the 727 and perhaps even the 707.