2x on the spacers. There is a FSM spec on end play of axles. I think its around 1/16". Too little play and the clip wont go back on, too much and you will have a rear axle clunk from time to time.
Generally the old spacers can be reused. They are also available at the dealer if new ones are needed.

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1985 300 TD 448K
1984 300 TD 278K

1983 240D euro 240k
1994 f-250 idi turbo 330K
1986 f-350 IDI
1987 F-350 IDI

1985 JD 1050 4wd
1965 IH 3660