Cloth covered wire

[Rafael Floresta]

I am evaluating buying this property. It has a cloth covered wire, from the 60's. 

The wires have ground in them, and they run all three cables (hot neutral and ground) inside the same wire. They seem in great condition, and I am wondering if I should replace it since I am going to rehab the place. Code says if you are going to rehab you need to bring the wiring up to code. 

I am interested to know if the code is specific to have the NM wire cover being a plastic/pvc cover, and if those wires from the 60's have the right gauge by code.