Yes. In the late 40s to early 50s the Ontario 25Hz system was converted to
60Hz without too much problem in most appliances and transformers. Many of
the modified 25Hz metering devices were only tossed in the early 90s as they
were beginning to not pass the tighter accuracy specs brought in later.

I believe you are correct about 50 to 60Hz transformer usage as the iron
size would be way oversized. It is different going the other way (60 to 50)
Typically the laminations were not much different to cause any excess
heating losses in the cores. It`s been a while for me on this subject. The
winding ratios determine the voltage inut ratios and the current ratings
of the conductors don`t change.

The standard N. American voltage spec is 120, 240, 600 (Some parts of
Canada, not familiar with 440-480 though) + or - 10% at the customer`s
panel entrance. AFAIK it has always been that but much confusion has
happened over the years.

The only place I have heard of 135v is on rural light bulbs so they run
cooler and the filaments last a long time and are not as critical with
surges. We may be confusing appliance and device voltage ratings with system
supply specs mandated by governing bodies. Sometimes the voltages are
reduced to express what people think are at the receiving end. eg. 550v

Network system supplies used in apartments and downtown Kit. run 125, 216 in
order to satisfy the specs using 2 out of 3 legs on a 3ph 4w system into
residences to reduce the conductor size to deliver it to multiple units in
close proximity.

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My understanding is that you can run 50hz transformers on 60hz without
any problems - the higher the frequency the less iron required.

And as far as the voltage is concerned, 115/230 has been a standard
voltage in many areas of North America over the years. 117/235 may
not have been an official standard - but was also common in many
areas.

135 volts was also provided in some areas for rural electrification