Jerry,
On my old Interstate I took off the original chrome covers and put on some 4" chrome truck stacks. They slid right on with a little soap and persuasion. Maybe that may work for you as well. You could get them in a variety styles including a slash cut.
If you do a search on the general forum you should be able to find the company that sell them.
Now that is a good idea! I bet I could easily cut the end of the triple tubes chamber, extend the pipe, and then re-weld everything. Would take some trial and error, but that would certainly push the pipes out and use the stock ends.