If he's waking at 6/6:30 and ready to go down at 10, I'd start with maybe 4 hrs of A time and work from there. So if he's up at 6:30, try to put him down at 10:30 (if he's done at 10, then start with 3.5 hrs of A time and work from there) for 3-5 days, then 10:45 (or 4 hr 15 min). yep, the general plan is lunch, then nap, so depending on what time he wakes and lunches, then your nap will fall after that. Most mums find 5.5 hrs or so to be the "magic" A time. For Abby, it's usually 5 hrs of A time in the am, and 4 in the pm (but she's always been on the high end of sleep needs).
If he fights the pm nap and its generally no more than a catnap, the long am nap (by extending A time) is definitely the way to go! Let me know how you get on!