If that bike originally had a triple and the shifter is still there, just put a 30 on and adjust everything and ride. You could put a 39 middle ring which might be more useful.
The 30 can't be "too low" for a steep grade. A 30x23, which would be your lowest gear, isn't as low as the 34x32 modern bikes have. Plus, you could shift to a smaller cog if you're spinning too much.
If the 30 works you can ride virtually everything while you decide if you want to change things and it's the cheapest way.
I have a triple bike I ride sometimes. It was built with 52-39-30 and a 11-25 cassette. A wide gear range and I've done a ton of climbing on it, at least a couple million feet.