Not sure to understand your question but A Port 49 <--> C Port 49 B Port 49 <--> D Port 49 will work since A,B are on the same stack and C,D on the same stack. vPC is only needed when the hardware is not stacked or configured in a VSS mode. If your goal is to plug a device into stack A,B and stack C,D and try to bundle the links , that won't work :
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