Sam Legend... The leading shoe is the one which " leads" from the cam to the pivot, in other words as the wheel rotates it passes the cam first, then the pivot. Check the shoes, if they are identical, put the thickest lining in this position, an easy way to implement Kiwi's suggestion.
Holding your breath and sanding the linings lightly to remove any glaze will improve the friction properties of the lining, as will making sure the pivot and cam are lubricated to ensure the shoes move easily. A good drum will be smooth, unmarked truly round. An oval drum can be felt on the lever, and braking is in a series of grabs.
The pivot may be in a slotted hole, so check if the backplate allows any chance to adjust the the pivot position. Trick here is to loosen the pivot nut and see if the pivot will move in a slot. Reassemble and apply the brake hard, the shoes will centre themselves and then with the brake still on, nip up the pivot nut. This depends on the backplate you have, worst case is a fixed location.
Operating lever should approach, but never pass the magic 90 degrees with the cable. There may be some adjustment on the cam/lever, depends on type. Some have fine splines, easy to adjust, earlier levers are a steel pressing, try turning it over to alter the angle.
Cable...any stretch in the outer is lost braking efficiency...your effort is wasted pulling the outer cable coils together, not applying braking effort.
The eBay shoes fit plunger A's rear and early S/A rear, not your 8" front.
Swarfy.
