Where is the heater fan located on a 70 Chevelle? Is it under the dash neer the heater core?

if memory serves me at all the fan is under the passenger inner fender

yep thats where it is and you have to drop the inner fender down a little to get access to all the bolts.
Philip

Well this is really the problem. I put a big block in a small block car. I don't car about air condition but would like some heat this winter. As you look in to the engine compartment you can see a big open vent hole with the heater duct on the inside. I believe I saw the openings for the heater core on the far left side as you look at the firewall. Am I correct in thinking that hooking up heater hoses to these conections and making sure the fan works will give me heat?

It sounds like you have parts missing. Find another 70 - 72 Chevelle and compare what you have to a complete unit, even if you don't use the a/c you need the whole air box to make it work.
Philip

Just go ahead and take the passenger side front fender off and save some time and skin.