Hairpins are for single crosswise springs, the Hup has two lengthwise ones. The stock axle would work if you can find some kind of hydraulic brake setup, but I would go with a newer axle, a Chev pickup, for instance. If you don't trust the old springs, any spring shop can make you some fresh ones. Softer, flatter, whatever you want.
I'm not a fan of MII stuff. The Lincoln will have bits and pieces protruding from everywhere past your sheetmetal and look like crap.
The Hup is a great looking old beast, make a great tourer, lots of fun ahead for you!