I too think you might be better served by buying the parts you need, rather than cannibalizing from another setup. It's hard enough to build, but I'm not sure how easily you would be able to transform the guts from one setup to another. Is there a reason you don't want to just get a more traditional box mod? For something as simple as you want I could kind of see buying something premade, much more easily and possibly for less expense.
Although if this is your "dream" and you have some beautiful housing in mind I'd say go for it, but it's probably going to be a more complex process than you might think, so as you are working on assembling what you need, I'd probably stick close to the modding forum and ask questions as you go..
Best of luck, whatever you decide on doing!
Anna