It will show backorder until 3/21.
This is pretty common when a new vehicle is about to ship, some part numbers get activated with really low prices. In the past I've bought things like new aluminum 4.6 blocks for $190. You get your parts, keep it on the low down, and no problem.
But in this case someone decided to get greedy and order 25 of them, mark the price up by a ridiculous 80%, and spam the forums about it. This pissed off the Ford racing guys who can't sell theirs until April 1st. So now all of the Boss parts are set to backorder status, ruined for everyone due to this person's greed. They didn't even do a good job of being greedy, could have bought assembled Boss longblocks for about $5k instead of piddly intake manifolds.