This is a great discussion. First of all, I have no doubt the grip is period and authentic but I'm still convinced this is simulated ivory:
1) There is no 'ivory' age to this piece (i.e cracks, striations, yellowing). It also has a 'soft' look to it around the edges.
2) It too closely resembles simulated ivory grips with the same type of uniform deep grain but no other ivory characteristics per #1
3) As Ed Martin and Stratocaster state most ivory grips are ivory throughout. Bonding the trolon insert to ivory seems very risky given the brittle nature and changing/shrinking composition of ivory over time.
4) Because the trolon insert has remained intact and well fitted,IMO it has been bonded with some other simulated substance; and if you look at the top trolon piece it hasn't been inserted but rather bonded to the surface.
5) At one time the trolon insert and grip matched. Unlike trolon and most ivory, simulated ivory grips don't change colour over time.
http://www.ebay.com/gds/How-to-Tell-if-I...10311348/g.html 
