Yea I saw that price....crazy!
Do we know where International obtained their window regulators back in the 60's? I'm wondering if they are the same as what ended up in GM autos. Easy to find GM regulator springs.
For the price it is worth the risk to test one out.
Since the force the spring will exert is a function of it's wire length, width and thickness multiplied by the deflection, you should be able to estimate whether or not the ones here will be adequate when compared to your old one. Looks like 6 wraps and the other wire variables are similar.