[Arran]

Ron;
  Have a look at what Edcor has to offer, they seem to have a larger selection of vertical mounted transformers, and their pricing is better then Hammond. I would also not overlook the option of using a transformer with a 5 vac rectifier winding, I think that would be a better idea then using silicon diodes, which, in addition to being instant on, can also short out. Keep your eyes open for other makes and models of radio chassis for a donor transformer, such as a junker post war radio-phono combo unit or tube type cabinet stereos, I've used those as organ donors before.
 I don't think that 45 to 90 seconds was enough to have damaged the HV winding on the transformer, it must have been damaged to start with. It was obviously a high hour set, and the victim of a lightning strike, it's also possible that some foolish person tried plugging the set in and powering it up before you got it, the brand Z 6X5GT may have been defective, or it may have gone to short thanks to a shorted filter or paper cap. That being said a 70 ma current rating is right at the upper limit for a 6X5 of any sort, though at least they did not completely ignore it like brand Z did with their 1940 line.
 I can't say that the 7 ohm primary resistance is wrong, given that yours was likely designed for 115-230 volts at 50-60 cps. The RCA Victor service manual I have near me now seems to quote about 9 ohms as a resistance for a typical power transformer primary, this is for a 105 vac -125 vac transformer at 50-60 cps, 13.5 ohms for a 25-60 cps transformer.
Regards
Arran