A Soviet Union that pushes Communism "to the Rhine" will probably result in Spain getting an offer to join NATO, which in this scenario they'd probably accept. As for why it didn't happen OTL, basically Washington wasn't fond of Franco, and vice versa. Spain did get aid from the US eventually, but not on the same level that other countries got Marshall Plan aid. One thing to remember also is the colonial issue. Spain had a few, but that didn't help matters. Washington made a point of pushing countries even in NATO, like Portugal, to drop its colonies.