Sadly you just dont get guys with stocky bodybuilder physiques running competent distance races.
Body's are very adaptable in the young.......and we respond very quickly to our training. If we run plenty of miles, we simply metabolise the fat and unnecessary muscle.
One of my friends at school took up bodybuilding at 17 and got upto around 14.5-15 stone of pretty solid muscle, then got into rugby. After university he took up distance running......and the weight simply flew off him. He must weigh 10 stone now and has run sub 31 min 10ks in his early 30s.
Distance competence seems to go hand in hand with sensible weight loss and a good training plan.