while that is basically what I did, I noticed the shorter belt didn't have a very good wrap around a few pulleys.
I discovered that a 5.7 hemi idler is smaller and allows you to use a different longer belt to get better wrap.
the path is hard to visualize and I have a hard time putting it back on every time, but it turned out to be a stock 5.9 length, but for a weird application. don't remember off hand.
if it doesn't bug you , then it does work without going through that. but I remember hearing a chrip of belt here or there and decided I needed to fix it.