I have found conflicting information as to whether or not this chassis requires an isolation transformer or not and nobody seems to have come back to say whether it has or not.
I'd initially started digging into this to see if the chassis could be just converted to run on 240v and started looking at the Sanken STRM6511. now typically the chassis using Sanken regulators of the STR series such as the STR30130 and STR2105 are all not capable of being put directly on the mains (as mentioned before) but the STRM6511 is not specified as a "voltage regulator" per se in it's datasheet, but as a "switching regulator" which seems to me is different than the other regulators... and does actually say "switch mode"
From what i've been able to dig up, apparently this chassis may be Sanwas kind of first crack at a "switch mode" power supply... if this is the case, then an isolation transformer would not be needed. unfortunately the one version of the schematic i've come across has a schematic that is the second most terrible i've ever seen and is hardly legible, i honestly don't even know why it's been included. if it was more legible, i might be able to ascertain if it is in fact, switch mode or not.
so... the simple auto-transformer MAY work... but i cannot find any information confirming or disproving the requirement of an isolation transformer... the service manual does not say either way, as such i cannot make a recommendation either way.
I mean you can roll the dice and see if the autotransformer type supply works. worst case, you have to source another STRM6511 and probably replace the AC input diodes...