OK - lots of info on here if you search:
1) You can get shutoff valves 3/4" and 5/8" inch respectively and splice them into the heater hoses in the engine bay under the fenders and that will stop your leak if and until you're ready to deal with the heater. I have the part numbers if you choose to do that.
2) Many folks mistakenly replace the copper elbow under the dash with a plumbing store fixture that is guaranteed to leak
- you need the RIGHT elbow from Paragon -- so check that first. (Bottom center item in the parts picture). It HAS to have the flanges on it!
3) If your heater has the original silver capillary tube - carefully remove it and keep it...the repro heater control valves don't use it (its unnecessary) but many chose to keep it and reroute it in a faked manner for originality. I kept mine.
4) Make sure your hose clamps under the dash are tight and correct, they should be Corbin clamps - if you mess with them get yourself a set of swivel head Corbin clamp pliers - it'll save you a lot of cussin'
5) Do NOT twist and force any hose connections on to their nipples, they break loose easily. A little slathering of silicone inside the hose ends and some patience will help you slide them on;
6) Read the attached article by Dave Z.
This should be enough to get you going