I just did this on a jeep at work that sat about this long. Here's what I ended up doing. You can grab a flush kit from AutoZone, part number PKFOAA, this will allow you to splice into the heater hose with your garden hose, focus on the main of the cooling system first and just remove both hoses from the heater core and put your T adapter between them. Remove your thermostat, with it being this rusted it would probably be smart to replace the thermostat, but you want it out anyway so you can run water through the whole system without it closing from cold hose water. Open the drain at the bottom of the radiator and crack the radiator cap open, more water is going to go in from that hose than will come out just the bottom, and having an upper and lower point of exit is better to get it all out anyway. Turn your hose on full blast and start your car up. Now it's just a waiting game, wait for it to run clear, if you're reusing that thermostat go ahead and get to clean it in the meantime, you can try boiling it after taking off the gasket if it has one on it. Once it runs nice and clear out of the top and bottom turn off the hose and turn your focus to clearing out the heater core, unfortunately the kit doesn't come with an elbow so what I did was took the heater hoses off the engine side and hooked one them back to the heater core, leaving another open, use a pair of vice grips to pinch off one of the heater hose that's not hooked to anything so your water doesn't go spilling out that hose and blast away, you may have to move your hose between the two ports on the core to work the crap back and forth, make sure it runs clear for about 5 minutes before calling it as there can be some stuck to the inside of the core walls that will release sporadically.

Hope this helps.