The oils that were available in the 50's were far different than modern oils...
If by "blends" you are referring to multi-viscosity... then Yes a good multiviscosity is far better 'today' then they were decades ago. They will also lubricate better than straight weight oil. There are a few reasons why, but unless you are actually going to travel back in time, the actual reason why early multi- vis oils were not always good really makes little difference, and if you do not know that multi-v oils outperform single weight you have not researched modern oils, Or you feel good enough will work fine for you...
Today your 1955 engine will work well with any good multi viscosity oil. It will last longest with a Good Synthetic Diesel rated multi viscosity engine oil...
The older 1955 oils were Not very good at cleaning up carbon and keeping it in suspension, there was a Lot of thermal sludge deposits and carbon build up in all engines... stay in the 2014's and future years to come, and use modern day synthetic HIGH detergent (diesel rated) engine oils. Today engine machining tolerances are a Lot better, so you 'may' have a lot of carbon build up in your older engine... but using any good Synthetic oil will reduce any future build up... (synthetics tolerate heat Much better & will Not burn to carbon, as easily as mineral oils. :smile:KennyV