Not completely. I'm fairly certain it was a joint venture between Case and Cummins. Case needed something better than the 336, 504 platform, Cummins wanted into the vocational truck and pickup market. They came about in the mid 80's. Case called them a 6T or 6-590 or 830. (T is for turbo, obviously) and same 4T or 4-390. Had Case on the nameplate, no CPL. Yes, the C-series came out the same time. Case used them extensively in construction equipment, CaseIH tractors after the merge (the 94 and 96 series tractors, Maxxim and Magnum tractors, and combines. Cummins put them in Dodge pickups and Ford and Freightliner trucks. Then they were called the B5.9 or C8.3. I don't think I've ever seen a Ford truck with the 5.9 though. Just to muddy things up even more, Komatsu used them as well. Called them a SD6-something or other. Said Komatsu right on the tag. -6 and some -7 excavators, D61, D65 dozers had Cummins engines.
Just my opinion, but I feel that the B-series is one of the best engines designed and produced ever in history. We had one in a 780C Case backhoe. Would start down to -10°F easily, no block heater or ether. Popped a radiator hose once. Got so hot the block turned color. Had a few hydraulic pump failures where the front hydraulic pump seized. Since it was mounted under the fuel pump and drove off the cam gear, when it seized it spun the drive gear on the crank. Bent all 12 pushrods. Replaced the dowel pin, drive gear, and all rods, back to work. That happened twice. Final failure was the camshaft broke right after first bearing journal. Figured that the bearing had been spinning in the block due to all the stress from driving that hydraulic pump. That happened at 9700 hrs. Engine at that time burned no oil, and started first piston up every time.