What would it take to install A/C into a 1973 220D that did not come with factory A/C?

What would the approximate associated costs be and will it be worth it?

Thanks for your responses.

HS

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1986 300E (3/2002) Rear ended and totaled (10/2009)
2000 Xterra (5/2000)
1992 400E (11/2009) -Sold
1986 300E (12/2009) - Sold
2004 E500 Wagon (6/2013) - Sold