Are there any differences between the auto boxes on a 420SEL and a 500SE of the same age? Different ratios or different bellhousing patterns?

I'm putting a 500SE engine into my tired 420SEL and was wondering if I should use my known good existing box, or put the relatively unknown condition 500SE box that I have in it?

Cheers, Martin

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1990 420SEL 217k Miles
1975 Chevy K10 400ci SBC power!
1995 Jeep Cherokee 4.0 Limited
1997 Suzuki GSXR750 SRAD
1989 Kawasaki GT550G4