Mine has a couple of plug-in transformers and certainly seems to have a balanced output. I've read that some of them came with a jumper in place of the transformer. You wouldn't have to modify your AM10 to make it balanced, just wire up transformers to the plug in place of the jumper. I think. If I'm already in over my head someone will let me know, I'm sure. There are some excellent resources on this site for buying new, decent and relatively cheap transformers. I don't know what the turns ratio or impedance of mine are. If you don't have a schematic, Google Ampex AM 10. There's a schemo that'll come up pretty fast. Let me know if you find any low noise mods. (I could have three more of these if this all works out for me, so I'm kind of excited.)
Keith