I have a CB500 triple that was lengthened to fit a 750 by cutting two stems to make a single weld in the middle with an interior sleeve, it's not up to the NHRA spec but that bike was raced all over the streets of Central Illinois and made more than a few passes down the drag strip.
When I got it, the top tree was broken by the pinch bolts being overtightened, but it never came apart.