I'd say the royer mic mod is a great mic for the cost. There are a lot of circuits that are great, it really depends on what you want to use it for ( vocals, acoustic instruments,..etc), what style of music, and how great of quality, or how much money is a value for you.
http://homerecording.com/bbs/equipment-forums/microphones/apex-460-capacitor-change-196274/39/
Loads of info, good and bad for modding your Apex 460 at the link above.
Enjoy the ride! 8)
If you look hard enough and study the schematics, you can actually mod your standard 460 to have into an exact replica of a C12 or 251 circuit with no need for 3rd party products! Although they do make life easier
Is it your first mic build? If so a mod can be satisfying because you usually start out with a working mic, so you can learn its good and bad points, and improve it in stages. And you learn stuff as you go along.
It sounds like you want a tube mic, so the Apex 460 is fun and good value, and the web is awash with mod ideas. I'd also vote for Dany's D-87 if you think a U87 style mic would add something to your setup.
For many people, mic building/modding becomes a bit of a 'habit' - so you'll probably end up doing several of the ones already mentioned!