Mike,
Sure, that's an easy one. Just remove every other part on the car and, when you are sure there is nothing else to unbolt, you will see the heater box (core).
Seriously, it really is buried in front of and at the top of the air distributor box which is at the front of the tunnel (inside the car). It is secured to the firewall, inside the passenger compartment. If you need to access the core itself it really is major surgery, and there are several threads on "how to". But if you just need to access the control valve and are lucky enough to have a later model sl then you can get to it from an access hole in the firewall (from inside the engine compartment). What exactly are you trying to do?
Best,
g
'64 230sl, fully sorted out...ooops, spoke too soon