Hi DavidLJ,
I am heading down a similar path as you with a EQ6 extension pillar bolted directly to the top plate of a pier. I have narrowed it down to two options:
1. Retain the locking disc and drill holes to bolt the disc on a new adapter plate.
2. Make a new adapter incorporating the locking disc portion.
The second option will be more expensive, but may be more solid
Anyway, they are my options below if anyone is interested.
Bo