I would expect a 123 chassis radiator to be a smaller size. If you measure the length and width though, you could tell for sure. Even new though, a radiator shouldnt cost that much, I would think $400 tops new.

Is a radiator from my 73 450SE parts car the same?

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1959 Gravely LI, 1963 Gravely L8, 1973 Gravely C12
1982 380SL
1978 450 SEL 6.9 euro restoration at 63% and climbing
1987 300 D
2005 CDI European Delivery
2006 CDI Handed down to daughter
2007 GL CDI. Wifes