toilet
Here is what the Sibley looks like, just in case you've never come across one:
Oh, we have seen hundreds like that, just not in the past 40 years or so, (and even then we usually removed them when we came across them, we did not install them). They had absolutely nothing going for them. They were impossible to snake when something got stuck in them, and they were an inefficient flushing design. How did you modify the toilet so it uses less water? You would have to have done that in the tank feeding water to the toilet. A flushometer doesn't need a larger line to build up pressure, it needs it to maintain the pressure while the toilet flushes.