Originally Posted by TheHeatKitchen
I would go a two shock system. No bionic arm at first. He battles Cap, Cap uses the shield, beats him down with it and ends up removing his arm. He unmasks him, revealing he's Bucky. Crossbones or whoever attacks, retrieves WS, takes him back to HYDRAs base or whatever. Steve is distraught, emotional, etc. They meet and fight again, WS is nonstop attacking him, reveals the bionic arm (think the fight in the tunnel from I, Robot).
You get the emotional "surprise" early, and the action surprise late.
I think you should get the action surprise first when Cap is battling WS. That will make him less likely to think it's Bucky. Then, when he does unmask him, the horror of the situation will hit him when he realises what they've done to Bucky. If nothing has been done in terms of mutilation and arm replacement, then it's not as big a horror to Cap.