I hope I'm not teaching granny to suck eggs, but you guys know what's going into those over-ready jobbies, right? Lux-rc.com has the integrated driver/led triples (choose your emitter and color temp). Lenses are by Carclo (various available; none of them are super-throwy with an xml edit: not xml, as Chicago X noted below... xp-g or xr-e. Doh!). Carclos are widely available.
If you want to live a long and happy life, you'll get the right connectors for the lux-rc boards, rather than solder directly to a 0.5mm post. Lux-rc has a wiring kit, or you can find the bits separately.
Diameter is 20mm, height is about 10mm with optic and lux-rc board. I think this would be a good fit in a p60 setting if you had the lathe skills to make a nice copper slug for everything to sit on.
Lux-rc boards come in 3 main configs: master, slave, and single mode. The master has modes activated by a momentary; slaves are driven only by masters, and singles only go bright, unless you dim them with some other means (like qtc). He's got 3 power levels: about 7, 11, 14 watts (varies slightly by emitter). Those have different battery demands to stay in regulation.
These aren't budget, exactly -- 50-70 bucks and then shipping -- but if you consider the price of a driver plus a triple, it starts to look reasonably sane.
They can be hot without adequate heatsinking. In still air, my 7 watt unit in an easy2led housing (here: http://www.easy2led.com/index.php?main_page=product_info&cPath=65&products_id=181&zenid=50e56dbaec009eb8d59079818158f54f ) gets too hot to touch. In moving air, it's fine.
The guy behind the affair is Quazzle on mtbr.com and CPF where his reputation is good. He's in Russia, which made me pause initially, but I've ordered from him a few times with no problems.
My apologies up front if I've gotten any of the tech info wrong... I'm just a happy (if under-eductated) user.