No problem, I enjoy working with runners.
Your core can be split up into two groups: global and local.
Local core refers to the deep postural muscles that stabilize the spine - muscles you cannot consciously contract (multifidus, etc.)
Global core refers to the muscles that flex and extend the spine, muscles you can consciously contract (obliques, abdominals, superficial spinal erectors).
Balance between these two muscle groups, as well as spinal flexors/extensors and pelvic tilters is essential to running economy.
So, a mixture of static work (bridges, planks, etc.) and dynamic work (twists, pulls, crunches, back extensions, etc.) is essential to developing a strong core.
If you PM me your email, I'll fish out some articles about training for distance runners and send them to you.
Br