Hi there,
Personally I'd recommend using Mobil Old Engine Superdrop 25W/60 SG or Mobil Early Model 25W/60 (can't remember its API rating, it may be SH). I used the Old Engine Superdrop for five years on the clapped-out grey in my EJ and I had no further problems with oil consumption despite the old grey's stuffed valve stem seals. Besides ....Mobil Old Engine Superdrop I have found to be retailing in just about every K-Mart for the princely sum of $16.99. I'll be damned if I'm gonna spend $25+ for that fancy Penrite stuff for a Holden which I don't use everyday.
I may be wrong but I have heard that with older vehicles, it's best to stick to an oil with an API rating which is closer or more relevant to the age of the car ie: SF=pre 1980, SG=pre 1988 etc etc. This may be due to such oils being more suited to the wider tolerances of older motors like the grey.
Cheers ...... Pete