A - I would say NO - a slow heart rate doesn't necessarily coincide with a slow metabolic rate. Your relatively low heart rate is due to the training you've already done which has brought about a strengthening of your heart muscle and as a result it is able to pump out more blood with each beat. This is why in elite distance runners you'll get resting heart rates in the low 30's.
But it also depends where you start with before training, since before training some folk will have a resting rate of 60 while others are closer to 75; and the person with 75 still might become an elite athlete and have a resting heart rate of 50. I believe the former world mile record holder, Jim Ryun, was in this situation.
So I would recommend you look more at your diet. So, with respect to your weight concern, I recommend you review your diet....and you may also want to check out your body composition to find out if in fact you should be losing weight in the first place.