Clock removal (What you see there is also a 1.0 xbox) : https://dcdalrymple.com/removing-the-clock-capacitor-from-your-xbox/ or if you prefere a video : https://www.youtube.com/watch?v=E9n4rnMekx0
The bios on the modchip should be a EvoX m8+ for 1.6 which can used in a 1.0 as well. How ever, you can reflash the chip with a EvoX m8+ (1.0/1.4 - 256kb)) made for this console. You can find those an any actual installer disc.
And ofc if your nephew dosn't have made the garden work for you, you can reuse the HDD if she is unlocked (If she is locked to the old console it dosn't work. You would need the 1.6 working again to unlock the HDD (Or you have a eeprom backup somewhere).
Soldering tutorial, hmmm. Here is a nice AiO : https://www.youtube.com/channel/UCA8cbDXjn-6ZkKE0f4JXDfg/videos
I guess that will cover anything you need to now (you just need some time) :