Replacing the Y-axis beams is pretty straightforward, replacing the drag chains is okay too, but wiring and testing should be described in more detail.
I've got the wiring right on the first try, but due to unclear instructions I had doubt about it until I successfully tested it. For example, the mainboard wiring diagram in user manual should be complemented with cable markers, and since there is that polarity reversing adapter, and instructions says that it is needed only if the laser doesn't light up, it should also remind the user there is another reason the laser might not turn on - the tilt sensor, and therefore it is important to put the electronics box back in the upright position (as if it was mounted on the machine) before testing.
I was really panicked as I thought I did something wrong and damaged my laser when I was testing it with and without that adapter, then I also tested it with the original cable, and still nothing, until I gave up the debugging and fully re-assembled it.
Also when I had opened the electronics box, the laser controler's cooling fan was dirty from the smoke, so you should perhaps make some modification to stop air intake from the laser side of the electronics box, and draw fresh air from the front of the machine instead.