I've read good reviews for IRD freewheels. I have a recently acquired 83' Specialized Expedition that I ordered a 7 speed 13-32 for. Stock gearing is 6 speed 13-30 out back with 28-42-44 in the front, which gives me a low of 25 gear inches. The new freewheel with front chainrings of 24-36-44 will give me a better spread and get me down to 20 gear inches. A little spendy but if it's quality and does what I need, that's a win.

I don't know if 120mm spacing will accommodate this, maybe someone else can weigh in. They do have a 5 speed 13-32 or 13-28.

You could potentially also reduce the size of your inner ring from 40 to something less.

Per this calculator (BikeCalc.com - Bicycle Gear Inches Chart) your current low gear inches is 44.

If you make any changes, you'll need to make sure your derailleurs have the capacity to accommodate those changes. I would think any change of at least 10% would be a noticeable improvement.