Oops, 1960, cable shift, cast iron case.
You need the appropriate FSM but I'm guessing the O rings will not be anything special. They hadn't even hear of metric back then.
I also have the O ring assortments, both Red and Blue and you look at them and tell me there's a difference between the O rings from box to box, the only real difference is the color of the box ;]
And at the same time, I would not trust an O ring from these assortments for this job, buy something of better quality than 1000 O rings for $20...
I'd try to shop with a transmission parts wholesaler/retailer for sensitive parts like these.
Mopar was well ahead of the curve on transmission sealing, using O rings, also by way of not using a vacuum modulator to set shift points like both Chevy and Ford, marching to the beat of their own - and much better - drummer.