I enjoy custom grips. I believe it is the only way to get a grip that fits my hands. Who has the "universal standard size" hand any way?
For years I have felt the grading system has been flexable by each merchant, ie, their "best" grade is the best of the current shipment, not the same standard year to year.
I have used the exotic cork rings. It is heavier and denser than real cork, but looks nice. Being much harder to shape than cork, I would not use a block. I turn on the blank and tapering the block's hole seems like it would be difficult.