Oh now now NormK don't be like that.I think there's other reasons they are changing to four strokes.Possible as they can build them at an 8th of the cost of making two stroke engines.
Anyway speedy I just wanted to let you know that your mower isn't a mustang.That particular base wasn't used for the mustang at all.It was more of a Corvette base or a Corsair also some store brands used that base although I think they were still a low arch.I know it has a Mustang cowl on it and I can see it doesn't have a snug fit like it should.Also it is an 80 series full crank engine so I know the carby wouldn't be a G4 it should run an LM carby. Similar but not the same.
This is what a 80 series mustang looks like,with that cowl.
[Linked Image]
[Linked Image]

These two model Mustangs ran from 1979 to 1981 (I think).Also they were the first model Mustang after the VC was dropped from the name.
And this one is the one that took over in I believe 1982.
This one however has been awesomely restored.
This mower is one from an ODK menber.
[Linked Image]
[Linked Image]
Just thought I'd let you know more about your mower.
Cheers.

Here for a good time,not a long time.