The shrinkage and bubbling in the wrap is common for the wrap on a lot of drum sets from that time in addition to Slingerland. (I had to replace the wrap on my 64' Slingerland kit for that very reason) The additional piece of wrap is also common and you can tell if the wrap is original by looking to see if the wrap is wrapped right into the shell. A lot of the bigger drum companies were making their own shells and would roll the wrap right into shell as it was being rolled. The badges on the toms were placed onto the shells without a vent hole at least into the 1970's so you would be correct on that.
I am going to go ahead and state the obvious here just on the off chance that you haven't noticed already. The kit is mix matched and has an RK bass drum is 1954 or earlier because it still has the beaver tail lugs on it and the floor tom and rack tom both have the teardrop lugs on them which didn't start until 1955. The date could be narrowed down by looking at the badges on the toms. It will make a good players kit with a little TLC. Good luck