What kind of sentence will this guy be looking at?
Presumably (haven't checked yet) he was convicted under the 1911 OSA, which specifically covers passing on classified information useful to an enemy or potential enemy, a definition presumably met by Iran. The maximum sentence is now fourteen years (it used to be 25 IIRC).
The sentencing judge will presumably look at the damage that he ostensibly did, his motivation for commiting the offence, and his previous record. Given that the information passed on seems to be of only moderate sensitivity, that he was seemingly motivated by a mixture of waltism and ethnic loyalty to Iran rather than venality, and that he has no previous record, then I suspect he'll get half the maximum sentence, so about seven years.
There was a case with some echoes of this in Bosnia in 93, when Milos Stankovich, a pathfinder captain in 3 Para who spoke mother-tongue Serbian, and who worked as an interpreter for BritBat, was accused of passing confidential information to the Serbs. He was thrown out of the army without being given the chance to see the evidence against him or answer the charges, which was deeply unfair. At least the MoD has given James the chance to defend himself in a trial.