FWIW, I was curious about what the MC for a '56 looked like. A little research and it's the generic single MC that Chrysler used on a lot of cars.
If you want to stay with the single, that's up to you, but a later double MC will bolt up nicely. I started crossing the numbers and found your MC also fit a '64 D100 and guess who did a dual MC conversion on a '64 D100? I ordered a later MC, and I spec'd the '69 Roadrunner MC. (just because I probably knew the part number back then).
So, that may answer the question that everyone skipped around.... Or at least what I think you were asking. Your Volare MC is going to be for a disc brake car and I would avoid that.
Again, your choice... Will makes a good argument for staying with the single MC, but I also remember the absolute terror I experienced while test driving a single MC car and having a hose fail. Granted, that was years ago and I'm sure the owners of that particular POS didn't keep up on maintenance. I have done the conversion several times, the last being my '65 Barracuda.
One factor that has me advise to do a dual MC has been discussed in many threads here, but never tying it back to adding a dual MC. The quality of parts is often questionable these days. Lot's of reasons, off shore manufacturing seems to be the biggest. I also worry about guys using NOS parts with 50 year old rubber in them. The failure rate, even with "new" parts is high enough to want to do the conversion.
But, your car, your choice.