Differance between 0030 & 0031

[buickGTP]

Can anyone tell me the differance between Buick/Dart/gn?
pn 25500030 and 255000031 aluminium heads .
Thanks
Steve

 

[BLACK MAGIC RACING]

I could be wrong here, but from what i've seen, the 0031's are set up for t+d shaft-style rockers, which oil the springs through a fitting in the head, through the shaft. THe 0030's i THINK were set up for jessel style pedestal rockers that oil through the pushrods. But like i said, these are only my observations and may not be 100% correct