Before we can discuss the straightblast, we must go over its history.
The Straightblast was a term coined by the late Bruce Lee for the chain-punching that he modified from his mother art of Wing Chun.
Jik Chun Choy, the original straight blast was thrown as chain punches,one over the other, in a thumb-up position. The footwork was a type of shuffling footwork where the lead foot always remained constant (i.e., if your chain-punched starting with the left foot, your left foot stayed forward, as your shuffled forward with your chain punching).
The Straightblast was modified by Lee because he found that the wing chun footwork did not give him enough momentum and leverage to apply PRESSURE with his punches.
So the JKD/Jik Chun Choy threw out the shuffling footwork from wing chun, and replaced it with an all-out SPRINT. In this situation, there is NO lead foot. Each foot switches leads are you sprint towards your opponent with your chain-punching.
The Straightblast is treated, nowadays, as less of a technique, but more of a CONCEPT. The Straightblast, in order to be effective, must achieve 3 key goals:
1) Apply constant forward pressure. It's not enough to hit him a thousand times if you're just standing there. It's not enough to move him back with just one punch. You must apply constant strikes with a sprinting pressure in order to...
2) Make the opponent go backward. This is crucial to the success of the technique, because, to paraphrase the words of Paul Vunak, there is no system in the world of martial arts that trains its practitioners to launch an attack while being forced to move backwards. Boxer, wrestler, karateka, judoka, all become "wounded cranes" when they are forced to move backwards for strikes.
3) The Straightblast must bring you close enough to apply the thai plum, in order to facilitate HKE (headbutts, knees, elbows). The Straightblast becomes a useless technique if, after making the opponent go backward, you simply let him go to regroup. If you allow him to do so, you give the boxer/wrestler/karateka another opportunity to launch an attack that is based on their style of training (a style that you may not be familiar with). The straightblast is NOT designed as a finisher (although some athletes like Belfort have used it as such).
To think of the Straightblast as a CONCEPT rather than a technique, gives its practitioner the FREEDOM to apply constant forward pressure with ANY tool.
Aside from Vitor Belfort, Manny Pacquiao brutally applied this concept of constant forward pressure in his first fight with Barrera.
It doesn't matter if it's chain-punching, or jab/cross/jab/cross/, or hook/cross/hook/cross, or stick/knife/stick/knife, or knife/sig/knife/sig, or landrover/landrover/landrover, for as long as you accomplish the above three goals of the straightblast (however, in the case of the landrover, I don't foresee the need for the HKE), the straightblast CONCEPT is a success.