I'm not here to start a war nor is there one going on LOL
Our Apex 460 mod is about transforming the mic into a plate follower C12 circuit, not a U67. We accomplish this by changing out the circuit completely in the Apex 460 as well as rebuilding the PSU to match the original C12 schematic. That being stated you can
install a K67 into the C12 circuit and it sounds pretty sweet. Not exactly like a real U67 but one hell of a microphone nonetheless.
Here's the C12/U67 mashup Crazy Love - JJ Audio
Here's the standard C12 we do: JJ Audio C12 - Amazing Grace
PS Both JJ Audio and Oktavamod are fantastic options to consider. Whether you are looking to build a new mic locker or if you want to augment your existing collection. Both companies are worth consideration based on their own merits.