I'll offer up a completely different solution. Autoweld will bend up any frame you can draw up from either 2x3 or 2x4 material. They can also furnish IFS systems or you could incorporate the IFS of your choice into your drawings, then source the pieces from a boneyard or donor vehicle.

This is an alternative to fumbling with an OEM frame and adapting it to the Hup or jacking around with the stock straight axle and trying to find a safe solution that will operate well. You can have an IFS, IRS, power rack & pinion steering and 4-wheel power disc brakes in the old girl.

As Don said, you are asking questions at the start and that's a good thing.

I might start off a project like this by sitting the frame on jackstands and mocking up the tires I would use and positioning them where they look best, then measuring the wheelbase and front and rear track to begin my drawings.
Here is a chart of measurements from OEM production cars and trucks that may be of interest to you....
http://www.crankshaftcoalition.com/w...ANGE_TO_FLANGE

Here's Autoweld's site....
http://autoweldchassis.com/index2.ivnu

Opinions between straight axle and IFS will vary predictably, but for my money, it would be IFS and modern components hands-down.