The heater core itself has two long plastic tubes coming out of it...so, the tubes and the core are all one piece.
Those are the tubes that pass through the fire wall, and are the nipples you connect the heater hoses to in the engine bay.
There is no "manifold" per se...and the core cost me ~ $35 or so from Courtesy Nissan IIRC.
The swap itself takes 5 minute, super easy.
The process of getting AT the mofo, which is flat against the firewall behind the dash, etc...takes hours.
Putting it all BACK takes a few hours too.
I imagine that a pro dash guy could do it in less than an hour, but I was methodical, and taped labels on all the wires and screws, etc...so I'd remember where things went later, as I didn't do it all on the same day.
If LUCKY, the only broken parts are at the ENDS of the tubes IN the engine bay itself, where you can reach them...and, fit a hose section OVER them to essentially patch the leak point.
If the break/leak is on or too close to the passenger side of the firewall, you're screwed and glued.
:angst-big: