Assuming your chain is properly sized @ 114 links, you will need 3 half links. Since you can only lengthen in link SETS (inner +outer = 1"), you'll need to (probably) lengthen the chain by 2 inches. You "might" get by on one link set, depending....
What I would do to measure-
Put chain on largest ring & cog-
Take 2 skinny screw drivers and insert through the links about 3" apart.
Move the screw drivers together and see how much chain slack you can generate.
Typical slack should be at least 1 link SET, but < 2 link SETS.
IF you are close to 2 link SETS, you should be able to get by with 1" extra.
Personally, I'd just get a new chain to avoid having to use the relatively expensive joining pins etc.
You could put it away in a plastic bag with your old cassette and use the pair together in case you want to retrofit.