, Buzz here. All our 757's have the forward spar mounted boost pump. It's barely accessible through the small panel you can open if you need to change it.
Things on the aft spar are much easier to get, assuming you have a tall enough ladder. The wheel wells and area where the shock strut retracts into give lots of elbow room - and even some light to see what you're doing.
The boost pumps have pickup tubes inside, so the fuel is drawn from what ever part of the tank the engineering guys plumb it to. Notice on the 737-300 series, all the boost pumps are in a row: center, forward, aft and they're on the lowest part of the wing skin. Pickup tubes allow the pump to draw fuel from the forward, or aft section of the wing.