Im wanting to do the same to a 63 ; I have a back-half for it already to be installed( cut out of another Nova) coil-overs ,ladders etc. Ill probably never drive it on the street; just something to experiment with. I took the front straight axle out of an old Chevy van , but its too wide. I believe the old 60s Ford vans were shorter and might work. A better idea is Summit; they have a universal straight axle set-up pretty reasonable. My problem is I dont weld but if you can it shouldnt be out of the question; it was done alot in the 60s. THere are better street set ups but I love the nostalgia thing myself. Go to Steves Chevy 2 Nova site to steering section; they have discussed this before.
I was thinking Summit but now that Im reminded it is Speedway that sells the kits ; and very reasonable. If you can find an old Econoline and can weld it might work too. 60s Ford van. Speedway has always had the fiberglass front caps too; it would be a good edition to the straight axle set-up. I dont know how the steering box will work out; Ive heard people using corvair etc. If you click on Steves Nova site they can give you the whole run down on the swap.