Maybe a better solution would be to install two bypass valves, one at 4 and one just before 5. Then I wouldn't have to plug and remove the lines, just simply turn the valve.

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Spencer

87 2.5L 190D Turbo 5-speed - 102k (Daily Driver)
82 300D Turbo - 145k - Light Ivory (near mint)

Gone: 85 300D Federal - mileage unknown