Hi,
I've checked and the following applies:-
VS 8 LAX 1745 LHR 1145 744 0
BUCKET CLASS AVAILABILITY:
J7 D7 Z6 W7 K2 Y7 B7 L7 M7 Q7 X0 N0
No Premium Eco award seats left, and little chance of them converting anymore.
System is showing no award availability for Upper on the 20th either, however you could ask them to speak to Virgin nicely and see if they will shift 2 of the apex Z class seats down to G class for you to use as rewards. No guarantees of anything.
As for the return, 2 Upper Rewards are available.
Thanks,
Richard