Get the Helm anyway. Now-go to your local Honda delaer Parts Dept and asdk for a copy of the pages for the heater unit, blower assembly/housing and ducting. The wiring diagrams are in the manual. You may need the connector tube that goes between the blower and heater housing-try a yard or dealer for it.
If the part you have has the trap doors on it and is connected to the hoses on the otherside of the firewall-then you already have the heater housing with its core. The cable that goes thru the firwall operates a valve-make sure it works properly. If the part you have has only an inlet and outlet duct and looks like it goes betweent he blower and heater-that is the Evaporator case andf it is not needed for heat-but could be used as the connector duct; just seal the tubing ports.

Hope this gets you started.