I don’t know which subaru build you’re talking about as I’ve not watched them all but there is a black car and a pickup they’ve done in recent videos and both required a lot of hard wiring and complex fabrication
They built the levorg twice, first time was exactly what they are doing with the Up but instead of levorg to levorg it was STI to levorg. That was pretty much plug and play..despite being full drivetrain swap and front end swap.
The second time was them putting a built turbo H6 into it which I'm guessing is the one you saw.