Which Freehub Body, spoke length?

The current freehub is a shimano Exage hub which has a 7 speed HG cassette on it. I rebuilt this wheel with a mavic open sport rim, 36 hole, as the old rim cracked. The freewheel mechanism in the Exage freehub is failing at the moment. I have an old shimano 600 hub but it has Uniglide freehub on it. I want to replace the existing Exage hub with the Shimano 600 hub and replace the freehub on the 600 with a new HG one. I see that it isn't that difficult find freehub parts, but which replacement freehub do I need for the old uniglide 600 hub?

Will any of these work? I am happy enough to stick with 7 speed as I don't want to buy a new cassette as well.

http://www.chainreactioncycles.com/Models.aspx?ModelID=1161

The other question is regarding the spoke length. When I rebuilt the wheel I used the old spokes, I would like to avoid having to do this again as they are in poor enough shape, particularly the nipples. I tried using the D swiss calculator but I can't find the exact spec for the shimano 600 uniglide hub, so therefore I am at a bit of a loss. Has anyone rebuilt with this sort of hub before? Or could any one point me in the direction of the specs I need?