BusyB with the 773ER doing ULH then they are going to need more than two pilots per sector. Unless you know something I don't, which isn't difficult.
Here is what I was thinking. Keeping it really simple, say an extra two LAX per day, gives approx 120 extra sectors a month. If a pilot only does ULH then they’ll do three layovers a month. So 4 pilots to do 6 sectors, 120 / 6 equals 20, multiply by 4 pilots, gives you 80 needed. Now there are of course holidays, F&DT limits, need for reserves, more than three layovers a month and the fact that not all flights are going to need 4 crew. So the above is only a (very) rough calculation, hence my guess at around 70.