Signal Generator Source Impedance

Gentlemen,

The service manual for this radio I'm re-aligning states to use an RF
signal generator with a source impedance of 60 ohms.  I have never
heard of such a beast. I have a 50 ohm RF sig gen and a 70 ohm one. I
thought that would be all I'd ever need, but now this spanner gets
thrown into the works. I'm not having a good day so far!
Do I need to make up a suitable impedance transformer, or can I
proceed with the 50 or the 70 ohm ones I have, whilst making some
allowance for that (and if so, how should that allowance be made?)

CD.