Wiring Harness for 1973 Duster

I'm thinking about getting an EZ wiring Harness or Painless harness for my 73 Duster, the original is butchered and I cant afford 700 for a new on from Year one. I'm new to all this electrical car stuff and i dont know nearly as much as i need to know to be able to put this harness in. Im confused on what the bulk head is and what it is doing. I keep seeing people saying they wanna remove theirs and stuff. Is there a benefit of removing this from the car ? Also i wanna know what i should prepare myself with before i go out and buy the new harness. All i do is take stuff apart and putting it back together so any information about this will help.

1973 Duster doesn't have a fuse block, i got it from a guy who turned it into a drag car. has a 360 la small block in it, all the wiring is cut or taped off.