I've also seen rather frequent equipment changes on this route. The last time I flew this route the aircraft was downgraded to the 764. I've also seen DL cut back to a 763 with only 24 seats in F. When this happens there are frequently paying pax who get bumped to the back and into a middle seat.
I pity the crew when this happens. The bumped pax's are practically levitating (myself included) and the FAs are left to deal with the mess.
I've flown the 777 to LAX and liked it, but now avoid it due to the frequent equipment changes.