will a 904 from a lil red express or a Warlock fit in a 74 Duster?

I have a guy that has (2) 904 transmissions- 1 from a lil red express and another from a Warlock. Will these fit in a Duster? I thought that these were more stout? Bigger? Geared lower? I have a 904 that was mated to a 360 from a 78 Cordoba. It had the lockup converter, but needs a good rebuild. Im trying to keep some gas mileage and the engine is a stock 360 2 bbl that was changed to a 4 bbl. Thats the only mod made-and a set of headers.
Will I have decent gas mileage but a better trans? Are they all the same trans? I have a line on a 727 also, but hoping to stay with the 904. I like the 904 and I wont be building this engine up to over 450 hp any time soon lol.