B plants are the armored ones, that's why they weigh so much more than the C or A. Now, just how much more damage it can take I am not 100% sure, but it scales with its weight, so since a C or A weighs 20 tons and a B weighs 32 tons, it's a fair bit more.
I like this one, I only changed a few things. I dropped the 7A Generator to a B to save 30 million(deck out a vulture for 21 million and a Courier for 10mil if you want) and traded a Chaff for an A Booster that gets you more shield strength. You can run the 6B scbank and a 4B scbank together so spam scb all you like to make up for the missing chaff. Bumped the sensors up with the remaining power from dropping the thrusters. If you want dual beams drop your thruster to C and sensors to C. If you want the Beam without dropping to C thrusters you can trade a booster for chaff to get the 2nd beam and leave the sensors at B.
Some of the crazy prices on the highest grade items are just too funny compared to what you get. Did you know they make a 7A Fuel Scoop for 91,000,000... almost suffocated laughing so hard.