Impedance matching with transformer and resistor
Yes, 0.048 is the voltage/turns ratio for that TGL 35/001. (I have no idea why it appears in that TME photo to have so many winding taps though, when data seems to suggest there's only one primary and only one secondary.) So the impedance-transformation ratio is the square of this number.

As for adding a resistor on the speaker's side: that's only ball-park estimate because the speaker is also inductive, while your 10-ohm resistor is mostly not so. To make the matter more complicated, the phase shift (of the speaker) varies with frequency. If you're worried about overdriving your amp, then start with a bigger resistor value, and see/measure what happens in terms of temperature/current.

On the good side, the primary of this transformer probably has has high DC resistance. This gets added to what gets reflected from the secondary. Furthermore, the secondary has its own DC resistance, and this also gets reflected to the primary but multiplied by the impedance transformation ratio (i.e. you add it to your load and series resistor). Unfortunately I don't know what values those have for your transformer. They give the suggested impedance loads on both sides, but that's not necessarily the winding resistance. This is a rather poorly documented transformer, I should say. You can measure this stuff that's missing from the "datasheet" though, if you have the transformer already.