They are called weldable bungs. As for the dip stick, you can also make it on the top with the same method. Either one will work. If you really want to get fancy, I can try to find the pictures of the sight glass device so you can see the oil and condition of the oil. I was involved in a truck body business at one time and learned a lot of the tricks of the trade. Only wish that I had learned to do more of the work, but that wasn't part of my job. I know theory, but sometimes it is the application of theory that I need to work on.... such as welding and painting.
As the fellow that I worked for in college once said.... you know how to pull the frame to straighten it, but you lack the ability to know how far to pull it and when to stop.... I had stretched a frame out of shape once while trying to pull out a kink....