[Arran]

 I suppose one nice thing about Edcor is that if they are building things to order you could probably get a replacement wound with the feedback tap, supposedly they have several hundred transformer designs on file, if you are lucky they may already have it. It's also possible that one of their stock transformers has a feedback tap on the secondary, although it's more common for one to be on the primary. It isn't really a big deal even if they don't, one of they old tricks to obtain some inverse feedback was to connect an RC network from the output transformer secondary to the grid of the first audio tube, I think that this was what Ron was thinking of. One thing to note though is that there is a tradeoff from doing this in an amp that does not already have it, you reduce the power output level and have to compensate for it somewhat.
Regards
Arran