How hard is it to change a heater core in a 70 XR7? My local mustang mechanic wants $500-600!! The core is only about $40, but he estimates at least 8 hours labor to take out the dash and re-install. It sounds like too much of a headache to do myself(I live in an apt with no garage), but is it really that difficult? Would anyone else in the Sacramento area do it for less? This will be my second winter with no heater if I don't get it fixed, last winter really sucked. The cold is bearable, but the foggy windshield gets downright hazardous (especially with 3 passengers at night).