I finally had someone on the Facebook XR4 group post an image of a SiCo lower transmission mount as installed.
A reminder of the parts-image I found on an eBay listing:
A now this image of the same kit installed:
That looks like a
C-F-M LR Focus Transmission Mount to me.
Although in an earlier pic, it looks like a standard
LR Focus lower trans mount with a
Powerflex Insert was used:
Luke