Welcome aboard goose, this is the right place
Im having a little trouble following what the end part is going to be but ill try to help you out.
What version of SW are you using currently?
Some basics. You have 2 major file types to work with, Parts and Assemblies. When you create a part, it can be a single solid body, or multiple solid bodies(or surfaces but we wont talk about that for this situation). The modeling approach is very different from Acad as you said. And one of these difference which you have found in your case is History. SW models are based on parameters and the features in the model tree. Think of it as sort of a timeline. If you delete a part, you are deleting everything in the tree associated with it, and that means any of those features you used to create other things. There is a way around this. At the top of the feature tree there will be a folder called "Solid Bodies". If you expand this and right click on the body you wish to remove you will see a function called "delete body". This isnt the same as the delete key, but rather its a feature that gets added to the tree. This means everything dealing with that solid before the "delete body" will still be available and usable.
If you can maybe break down the design of what you are trying to do I can walk you through it step by step. Im just a little unclear on where the two parts are and what features you need to use from one for the other.