I would say at being 48"ish long to step up your size as well. If you already have the 2x.25 tube maybe could try to sleeve some 1.5x.120 inside them to save buying something else bigger. Might be hard to get to sleeve that long and need to take note of length of weld in bungs to compensate for on each end.
I run 2" .250 wall on all my suspension 4 links with 1.25 heims and 3/4" bolts no problem. Just try and make sure your link brackets are at least at the centerline of your axle higher if you can. Every link setup is different and to get the correct link separation you'll have to tweak with it. You may know or not that there are a lot of factors in acquiring a good working link setup they will greatly affect how the rig performs. Do it once and be done! Cheers!!!
I have 2" x .25 heated chromoly lowers and they are nice and straight still. My rears are mounted low on the axle tube with the idea of them hitting first than my driveshaft on my low pinion rear along with getting optimum separation on my old setup which isn't so relative now.