Hi Eric: Well, this certainly would be considered totally "cured" LR if it's been in his tank that long. Just know that you are taking a chance of introducing some unwanted critters into your tank by adding this LR. Have you seen this LR in his tank & looked for any obvious things like Aptasia for example? That is something that you definitely don't want in your tank.
In any case, I would only put about 60 to 80 lbs. of LR in your tank if I were you. You don't really want to load the tank up with too much LR. That being said, as long as you make sure that the SG & water temp are the same as in your tank, then I see no reason why you simply can't add the LR all at once without much worry. However, I would suggest doing a large water change around a day or two after the addition of this new LR. Good luck & let us know how you make out.