Hi Steve - Is 180 your ‘natural cadence’? On a run, without efforting to keep your cadence at 180, count your steps for 30 sec, and see what your cadence is. If you land above 170, go with that. If you land below 170, work up to above 170 two beats increase per week. THEN see what your heart rate range is at the cadence your body is more comfortable at. The reason I say all this is if you are not used to 180 spm, and you are trying to do that AND keep your HR at 130, that would be pretty much impossible. Make sense?
If your ‘natural cadence’ *is* around 180, then yes, you will need to slow down to 12 min miles for your long runs. Actually, that sounds about right if your half marathon was at a 10:30 pace (see here The long run is about endurance (learning to use fat as fuel) and time on your feet, not about speed. Your shorter runs and especially your speed workouts will help in the other areas. Hope that makes sense!
Certified Chi Running and Chi Walking Master Instructor