ZB34 - all alloy engine?

[icarus001]

I was browsing bikes and I came across this, it's a bit pricey but I expect that's not far off what it would cost to make a concourse job.
But I thought they were all alloy engines and that doesn't look like alloy?

http://www.carandclassic.co.uk/car/C845126

[chaterlea25]

Hi,
The ZB34 had an iron engine at first, then the alloy became an option, before becoming standard fitment on the competition models
Those early alloy components were not without problems,
The couple of heads I have seen seem to have casting defects repaired by welding at the factory ????
The 500 cylinder alloy muffs crack at the centre front or rear where the alloy is thin 
Lovely bikes to ride though 
John