Yes. The third bolts in. Their exactly the same, but to get one in a semi-floater, you have to take the center out so you can get in there to put the c-clips on the ends of the shafts. On the full-float, you don't have to take the center apart cause there is no c-clips cause the shafts are held in by the hub. Now if you are talking about diffs set up with ARB locks, again, a semi-float ARB will bolt in a full-float assembly, but the full-float ARB one won't bolt in a semi-float assembly. There are two ARBs for LCs, a semi-float one (usually for the rear here in the States) and a full-float one (usually for the front here in the States.)
BTW, BMT, where you at? I know of a FF rear that could be bought that's in Utah...might save you from $pectre's rediculous shipping charges (unless you are able to just pick it up from them...) got a rebuild kit for it too... And no, it's not the one that's under my rig... 8)
-Ferg-