I have not done it, but I have several used CXA holders that milled for larger tool holders. Shouldn¡¯t be a problem doing with a carbide bit. Maybe with a bottle of coolant to spry on the cut.
I use an Aloris BXA tool post holder on my Heavy 10, with great success.....up to now. I bought, and then discovered, that the BXA-22 Universal Turning and Boring Holder is too big, specifically too tall, to work with my lathe. The tool point is about 1/8" above center with the block down on the compound. I touched the holder with a file, and it seems pretty hard. Anyone ever machined down an Aloris tool holder?