G'day Maxwestern,
Thanks again for all the help mate. I went outside and got a photo of the side of the cylinder head with the stamped numbers on this mower as you mentioned. Looking at the rusted on nuts on the head I don't think it's ever been removed at all.
The stampings read:
398That other thread was also a good read, I noticed this Corvette was also featured on the other 2 newspaper ads from 1978.
What was making me think it was a bit before 1980 was that sticker on the top of the metal cowl which says "Victa Hi Torque 2 Stroke Engine" on my mower. In the 1980 Victa brochure you can see the larger sticker in the same spot on the Corvette which probably says "Series 80 Engine" or something like that.
Cheers and thanks for all the help with this it's great!
