Nothing that's going to net you a noticeable increase, I'm afraid. However, if you have the time to spare you might as well play with it.
You can do the general stuff, like port matching (assuming the stock manifold doesn't match the head) and adding a fillet/ smooth transition to any connections that can use it. You want mates surfaces to look like this(as seen on Ken Rockwell's site):
and couplings/ transitions to look like this:
Can the exhaust be wrapped easily? I'm unfamiliar with the 190D