Wiper question

[40plmczy]

Once again my car ADD has kicked in again and I got to thinking about windshield wipers. What set this off was someone posted about Newport Engineering wiper kits on another forum and I went to their site to see if they had a kit for my 40 sedan. Now my question is the wiper arms that were on my car are not complete and I was told to use 46-48 arms as you can get parts easier for them. I seen that Newport's kits are different from 40-46 to 48 plus you have the difference of vacuum versus electric. What is the difference between the years is it just the wiper trans arms or ? Whats the difference between vacuum and electric besides the obvious? I have a pair of 48 plymouth arms and pivots I was planning on using and I also have a set from a 46-48 mopar that have a nut that screws down on to the splined shaft but I don't have the pivots for them. Sorry for so many confusing questions as I'm trying to learn about the older mopars and what may or may not interchange. Thanks, shawn