Hallo master991
Original hole
Images thanks to drive2.ru (Russia forum).
My way
Video image
The square hole cut (19x13) should be perfect, then adjust with needle file set (bit to bit) until the structure fits tight (check again and again during filing). The light fastening tabs fit perfectly in this/my panels (click).
The work must be done by the interior/non-visible part of the panels. Never use the tools from the visible part of the panel (risk of scratching the panel), i.e, don't introduce any tool through the square hole from the visible part of the panel.
It's easy to do, requires patience and precision.
By other side, the best way to know the difference between one light and another is by buying them and doing a test with a power source. (about 10€ each)
Without any scientific precision I would say that KT1 is 25-35% brighter.
The next video is an example:
I did several tests with different lights, in the dark and with daylight, but my camera does not accurately capture the dim lights in the dark. (when I try to record it to make a video I get angry by the results of the recording )
I still can not make an assessment about the brightness of this lights once installed. It's the beginning of a project that is in relation with others due to the electrical installations (wires, panels, etc), so it will take me a long time* for all the projects to be finished.
* Considering that I'm now on vacation and the space/time to do these mods is more relative than ever (E = mc2).