check this thread
diff, all you need to know
in short the answer is yes. it will bolt staight in and yes the Ford gears will fit as they come from the same diff (BW78)
however, the VN diff is 52mm wider then your VH diff so the wheels will stick out of the gaurds, the wheel track will be all wrong and won't pass inspection unless you get some real odd wheel offset, much like a front wheel drive car so basically you would need to get the diff shortened. for the driveshaft you would need to use the rear section of a VN driveshaft fitted to the front half of your current driveshaft at the CV joint.
if your currrent diff is a drum brake setup you will also need the handbrake cable as the cables are different between drum and disk brake configuration if memory serves me correctly.
what is the reason for the upgrade? there are 3.55 gears avail for the large salisbury and there is a crowd that does a 4spider LSD unit to suit the large sals to replace the standard 2 spider LSD which was the weakpoint of those diffs
308 VH SL/E would a had 2.6:1 diff ratio, with 3.45 gears it should take off like a rocket. cruising revs with the trimatic might be a bit high though