In reply to Street:
There's parking at SH 62248 15761 which is a small lay-by next to the main road in Barmouth, I've left the car there many times before for 2 days or more, and you can end your traverse by coming down through the woods (Orielton Woods) straight to the car.
There's also the Panorama Carpark as well which is at SH 62488 16597. You can get down to this road from the hillside Radio mast below Bwlch y Llan above Barmouth.
Jason