Ian,
That's right, I do recall hearing that Bill Diddle did some work at Hamilton.
As for original Colt greens, sixteen doesn't "seem to be" original to me. It borders Robinson's first, which leads me to believe there could have been some change to sixteen when the new nine was added. Dick?
And nine green is messed up. Again, it seems to me the area where those little "pot" bunkers on the right are was originally putting surface.
There are indeed a number os WORLD-CLASS holes at Hamilton, including 3, 5, 6, 7, 8, 10, 11, 12, 13, 17, and 18! That's not bad, eh! Eleven of eighteen holes = world-class!
Last, I don't think you need to cut down any "protective" trees in order to restore a heathland sensibility at Hamilton, Dick. Sunningdale, for example, is quite heavily treed these days and still possesses a rugged, natural, heathland look. Simply restoring the bunkers at Hamilton to their original style and locations would go along way to achieve that goal.
The bunker inside the turn at number one, for example. The bunkers in the hillside, short off the second tee. The short bunker off the tee at the fifth. And so on...