Hi DogWalker. Welcome.
As much as I hate to agree with halhiker

Marion really isn't a bad trail. While it is steep, it's only 6 miles, and if you pay attention to the signs at the trail junctions, you'll be fine. It's also easily accessible from a good paved road.
The views from Fuller Ridge are excellent, but the dirt road winding back to it takes 20 to 30 minutes, and I'd rather spend the time on a trail than in the car, so I've only done it a couple of times. For the same reason (drive time) I have generally done Skyline or occasionally taken the tram when I come up from the other side, so I can't help you with other approaches.
In any case, don't let our postings make the trail sound obscure or difficult. We were just talking about a couple hundred yards at the top that sometimes confuse new hikers. If you come up Marion, when you head back down (going south) from the peak, you're actually going perpendicular to the trail, so it would actually be hard to miss. Once you bump into it, simply head west. Since you're experienced, you can probably find west, even without a map and a compass.
(One of my teenage daughter's friends asked me where the north star was. I pointed it out to her, then she asked, "So where is the west star?"

Hmmm. Unless you're checking star charts to find the west star, you'll be fine.)
z