Here's how I'd use McBride:
First game, against Czech Republic (OUCH) he should start. Depending on how things go, play him between 65-75 mins. At this point, what US soccer fans have to understand is that we have a BIG dearth of proven goal scorers. Eddie Johnson has been great, and is very young with young legs, but he's been unable to stay consistently healthy. If he's at 100% come WC, he'll start next to McBride, no question. At that 65-75 minute mark, though, I would agree with you that, at this point, Twellman is probably the first forward off the bench. McBride is used to logging lots of minutes and his level of fitness, playing in the EPL, is still very high, his age notwithstanding.
Beasley and Donovan will both start, obviously.
Here's my starting 11 for the WC:
Cherundolo -- Onyewu -- Pope/Berhalter(that's a toss-up at this point although I'd probably give the nod to Berhalter at the moment with Pope as first man off the bench -- Bocanegra
Midfield: This is another tough one, For the right winger at this point, you probably going to see Ralston, but if Clint Dempsey can play like he did vs. Norway in the remaining matches then I'd love to see him step up to that role, Donovan, Reyna, Beasley
Forwards: Eddie Johnson, Brian McBride