Under the air filter. Looks like I'm missing a loop (back air cleaner) and the heater hose has fallen out of the one loop in the left of the photo -
I thought it attached to the fender well here, maybe mistaken -
And attached back to the lower radiator hose or in this case the aftermarket water pump.
Does your J13 not have the outlet in the head with the return in the block? Here's a pic of my J13 -
Outlet in head TO heater core, top. RETURN in block from heater core, bottom.