FWIW, I tend to go with the multiple truck theory. At the very least, there may have been 2 trucks, one that the government knew about (the one checked by the marshalls in the alley), and the one that was detonated.
Remember the discussions way back of the possible fed look-alike? I still suspect that McVeigh was working for the government, either defense or CIA--and that he expected the sightings of the look-alike to be his alibi if anything went wrong. The feds gave him and Nichols up because they had to prosecute somebody, and McVeigh and Nichols were the most expendable.
I don't have that written in stone--It's just the way I see it at this point.