If your Mallory is the 2 piece cap they can be pricy but they do show up on eBay and if you are patient you can get one for a good price. There doesn't seem to be a big demand for the 6 cylinder ones. the rotors are the same. I just converted a Pontiac V8 Mallory to fit my 153 4 Cylinder.
I've been playing with the Borg Warner ODs since we put my son's '54 Studebaker together in 2000. I'd run them before but had never put one back together. With a supercharged 300" Stude V8 he was pretty good at taking them apart.
The best one for you would be the '67 and later Saginaw OD but they are rare and expensive now. The ones that were used in '57 would be fine. They are plentiful. They are not sincro into low but with the OD that is not an issue. All of the in tranny ODs were Borg Warner and they all work the same. Most were R 10s but some heavier duty R 11s were also common. I'm not sure about length. There would be some wiring to do and a cable to make it work like stock. I'll attach some links that will get you started. These are fun to drive. I'm going to use a Stude BW T86 with a Jeep T90 top shift in my '26 Chevy roadster with the 153.
WIRING OD TIPS Ford Link
