Thank you Tastyger, Sparrett and Giblet.
I am certain that the Mangles John Piper is my one but beyond that the only confirmed item I can come up with is the death notice from the Sydney Morning Herald (19/06/1856) which states "
June 18th, at his residence, Pitt-street, Sydney, Mr. John Piper, native of Toppesfield, Essex, England, aged 45 years." This is all correct for my John Piper and as he is the only John Piper from Toppesfield (small village) that is unaccounted for it must be the one that was transported on Mangles.
In Tasmania at the time there appears to be two convicts called John Piper one from Mangles, one from Arab, the one from Arab appears to heve left Tasmania early 1846 leaving, to the best of my knowledge, only "my" John Piper there.
I cannot confirm the marriage at this time as the certificate that Tastyger found does not give details of family so I am a bit stumped. The certificate has JP as 7 years younger than he actually was but I have found that is nothing to worry about especially if the wife is younger
So did my JP retrain as a boatman. I can now look for JP's leaving Tasmania as crew rather than passenger I suppose.
Thanks so far for the help, it really is appreciated.