I recently purchased the leather TEQ shift knob pictured below. I love it! The problem is, I bought it for a newer Toyota that uses the now-standard (for Toyota) 12x.1.25 thread. Unfortunately, this knob is older than that standardization (I haven't measured, it is either 10mm or 8mm). It fits my 74 Corolla, but not my 2000 Celica. The inside of the knob is not threaded, but is rather a soft plastic/rubber material. It self-threads when installed. The opening is so small, however, that I cannot fit it over the 12x1.25 shifter.
I need some opinions here. I know these old school JDM parts can be pretty valuable, and I don't want to ruin this rare piece. It almost looks to me that the plastic/rubber insert could be removed, but I don't want to break the knob. There is plenty of space in there to bore it out to fit. Would that be foolish? Logically, even though that would make it too big to fit an older shifter, an adapter could then be inserted. Best of both worlds? Or is it simply destroying a good piece?
Any advice would be appreciated!