[Arran]

It has to be a transformer designed for 60 cycles, if it's out of a switch mode supply it will not work, the frequency is too high. Since model 70s have a full wave rectifier you will have a 120 cycle ripple, so a 50/60 cycle transformer primary will be safe, you can use a lower frequency device at a higher frequency but you can't go the other way or the core of the choke/transformer will over saturate and burn up. In terms of filter chokes I think that a 50 Henry one would work fine, as long as it's 125 ma at least, it would be large enough to filter out the ripple and offer a similar drop, if not you can add a resistor in series with the setup as Mike suggested.
Regards
Arran