Complex sentence: Haanstra agreed that GPD would produce the low-end model of System/360 that became the Model 30, however he was not fully on-board with the "New Product Line" (NPL) as System/360 was known at the time.
Split into simpler sentences: Haanstra agreed that GPD would produce the low-end model of System/360 that became the Model 30. However, he was not fully on board with the "New Product Line" (NPL) as System/360 was known at the time.