Yes those ebay drivers would be fine but it would be better paired with smaller 6V XHP50.2/3 LEDs at 4A current. Or Osram WF1 LEDs wired in series, two per driver.
Putting a bunch of emitters behind single large lens is not a good optics solution. Each LED should have its own optic.
That thing didn’t produce a beam to speak of. It was basically a giant mule because each LED did not have its own optic.
It is not very tricky to focus an LED in a reflector, depending on the LED and reflector. For centering you can often just eyeball the LED on center and that’s good enough. For focusing, adjust the height of optic/reflector until the beam looks good or your lux meter shows the highest readings. Shim the reflector to this level. If the array consists of identical reflector / LED combinations they can all be shimmed the same. There are also centering gaskets available for some LED/reflector combinations. For example this + this from the Convoy store.
Is the battery going to be in a running vehicle or is it removed from a vehicle? A large subwoofer / car audio system capacitor may be advisable to smooth the voltage spikes than come from vehicle electrical systems.
If you switch multiple drivers at the same time from a single switch they can get out of sync if they are multi-mode drivers. A single-mode driver will not have this problem. There are some applicable drivers on KaiDomain. This one or this one can provide 2500mA, which is not a lot of current and is best paired with three Osram WF1 LEDs in series per driver. Small LEDs like this work good with small optics.
C8 reflectors are cheap and there are centering gaskets for this combination at the Convoy store. Or an L21A reflector with 9mm hole and matching gasket. Convoy offers some glass windows too and an aspheric lens offering.
Taskled Ultraboost is another driver option, but again XHP70.2/3 isn’t the best choice for this driver, and it will only be good for ~120W of LEDs at ~12v input. Taskled also has some buck drivers such as H6CC.
You can get an idea of the voltage and output characteristics of the XHP70.2 in this thread and this thread.
XHP50.2 test threads here and here.
Osram LEDs tested here.
If you’ve got a lathe you can make your own centering gaskets. They aren’t entirely necessary but they do make things easier. Adjusting the overall height of the entire reflector array by moving the frame / bezel is another way to achieve focus.
There are a lot of combinations of LEDs, Optics, drivers, etc. that you could use to make a monster sky beam. Kaidomain has a lot of reflectors and optics and stuff. Glass windows too. Many people use plastic for these larger projects for the front window since they can cut it to size. flashlightlens.com can cut large custom plastic windows from optical grade plastic.