The GP30B I referenced was a concept that never truly took hold. The carbody B-unit, like an F7B or a FB-1, were designed to head off labor demands that every locomotive have a crew. If a unit didn't have a cab, it didn't need a crew.
But as the diesel locomotive evolved, the wasted potential of all those B-units was realized. They had hostler controls for moving them around the yard, but couldn't be operated independently over the road. That meant if you were running a bunch of light trains that could be handled by a single unit, you either had a yard full of B-units not being used, or you were using an A-B pair that you didn't really need to use on the train and burning extra fuel. So as the labor laws were ironed out and the industry shifted towards the road switcher, all of those had cabs, which greatly increased flexibility. Now, you didn't have to worry about pairing up certain units in a certain order with each other. You just added road switchers to a consist until you had sufficient power and then the crew ran them from the lead unit.
But then the lines with more rugged territory that ran M.U. heavy trains began to come full circle on the thinking and asked the question: Why build and maintain expensive cabs on all units when they're used only a small fraction of the time? By cutting out the control stands, windows, cab structure and crew accommodations, they could save pretty significant amounts of money on a locomotive order. So in 1953, Santa Fe ordered 5 GP7s from EMD sans cabs. They were referred to as GP7Bs.
Then a few years later, Union Pacific and Pennsylvania Railroad decided they liked the idea and split an order of 165 GP9Bs. Again, identical to a GP9, just without a cab or controls.
While ATSF was on a B-unit hiatus, and PRR would never order another again, Union Pacific, who was running trains through the mountains with 4, 5 or 6 units loved the concept. And so they returned for 40 GP30Bs
UP also took 45 SD24Bs, which was the 6-axle companion to the GP30.
Power hungry UP wanted a 15,000hp 3-unit locomotive set and EMD responded with the DD35, a 5000hp 8-axle (two D-trucks) B-unit that was essentially two GP35 powertrains on a single frame with no cab, which was designed to be sandwiched between a pair of GP35s. UP would grab up 27 of these ridiculous booster units between 1963 and 1964, while SP would sample just 3.
Union Pacific would also convince Alco to build a single B-unit of their outrageous C855, an 8-axle, 5500hp Century series. It was very short-lived, as were the 2 C855 A-units and is hard to even find photos of
And then the idea went dormant for a while. For about 15 years, no one offered or demanded a road switcher booster unit. But everything old becomes new again and in the early 1980s, Burlington Northern, which had rebuilt a few wrecked units into cabless boosters (a common practive), placed an order for 120 GE B30-7ABs, which was a B30-7 (3000hp, B-trucks) with no cab.
Around the same time, Santa Fe rebuilt a handful of EMD SD45-2s into cabless SD45-2Bs.
And in 1991, Santa Fe would purchase 23 GP60Bs
These would be the last road switcher B-units produced. But, you have to wonder, if we are due for them to make another resurgence.