Hmm, last time I flew VA they landed at the Delta terminal, where they did a pretty good job at prioritising people with onward flights. Pity, because at TBIT they won't do anything for you.

Forget the bus, I lived in LA for 2 years, went to LAX a lot and can't remember ever seeing that bus. Go through immigration, pick up your bags (no checking straight through to MCO), go through customs, go outside the terminal, turn right and follow the road around to the Delta terminal (#5, one after AA).

Although mornings at TBIT are better than the afternoons, I still don't fancy your chances. At least you're booked through on one ticket, so they will look after you (and I rate DL above the other major US carriers).

Good luck!