somewhat pointless when a standard shimano freewheel remover costs peanuts.
OP - if the bugger is stuck on very solidly (its a standard anti clock unscrew), its good to attached the tool and reinsert the skewer to keep it in place, then either use a long wrench on the tool, which now wont slip, or even better hold the tool in a vice and unscrew the wheel off the freewheel - the tyre gives you a very good grip.
Steel freewheels last for yonks, but if as
I like Skol points out you are finding the low gears a bit high, they did do touring "blocks" back in the day 14-28 (as well as corn cob time trial ones). Going much beyond a 28T may give your rear derailleur range issues (even if you cold find one), and a lot of the period crank sets you struggle to get below a 38T inner ring on (a double). A touring triple is your friend in a hilly area.
the good news is frictions shifters don't care what speed freewheel you fit, so if you find a 6 spd 14-28T then that will fit just as good as a 5 spd.
At least you have a standard shimano screw on freewheel, one of my fleet has a Maillard Helicomatic hub, which is a whole other world of specialist tools and weirdness....