I noticed someone mentioned a 904 w/OD out of a Diplomat for use behind a /6. Is that correct or did I miss something? If this is right, what are the ups and downs of doing this? I'm not sure what tail gears my 70 Valiant has but it sure would be nice to have another gear on the highway. What other donor cars might be suitable for a tranny?

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70 Valiant Super Six

An A-904 with overdrive would be an A-500.

I could be mistaken, but I'm pretty sure no Dippies, Gran Furies or 5th Avs ever came with an OD trans. They were introduced in trucks in the late eighties.

D/W

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If it ain't broke, fix it!

No such thing. Diplomats (or any other M-body) never got an overdrive 904 (aka an A-500). Only pickups (and maybe just Dakotas at that) got those.

The Dips did get the A998 and A999, which are heavier duty versions of the 904 with lockup TC.

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The Dips did get the A998 and A999, which are heavier duty versions of the 904 with lockup TC

Will this tranny bolt up to the /6 or is there a bell housing adapter that must be used? What else is required for this tranny to work properly?

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70 Valiant Super Six

I don't think there was a slant-6 version of the 998 or 999, but as others have said you should be able to put 998 or 999 "guts" into any /6 904 case that had lockup (lockup requires an extra cast-in passage in the tranny case).

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there was a slant version of 998 999. I have one at home from 87 ram it has the electric lockup converter and all the other assorted non sense.