I would not worry about the numbers stamped in the heads. Not what the "valves are sunk" means. Regardless having new guides, and valve job done, and resurfacing the heads is not expensive compared to new heads if that is what "it's not worth it" was referring to. Basically confused by most of that but I if the machine shop is saying rebuilding the heads is not worth it go to another shop.
Cooling rail are the metal heater tubes that run between the water pump and intake ports to the heater core.
As for the fuel rails. They can be very gently polished with 0000 steel wool. Use something like WD40 for a lubricant....on the injector rails.