Getting back on topic...
Are the 379s 3rd rail "ready"?
As in, fit the shoes and it's good to go?
I believe, all that is required would be third rail shoes and shoe air supply/pipework, shoe fuse boxes, DC shore supply changeover switch, DC shore supply socket, DC mode contactor, Shoegear lowered governor and associated pipework, possibly some additional valves in the PTOSL, TCMS update and DC mode button fitment in the cab.
Edit: And High Speed circuit breakers
I don't know if any DC wiring was put in place at build (this has to go above the equipment cases on the DMOS's) like the AC wiring was put in place on the 3771/3/4/6 but the inter car jumpers should be set up for the DC bus already.