Quite possible to knock your stick out of "time" or proper location in conjuction of the shift forks. Basically, I had to remove the shifter, take a screw driver and pry the shift forks back into neutral postion, reinstall shifter and back to swapping gears.
I'm getting around 6 mpg with my 489. I built it to come alive 2500 -6500 rpm, and that's where she stays 90% of the time. I base it off how many smiles per gallon not miles per gallon though!
I must not be as hip as you hoss. But to answer you, thus was the case when I dropped my 489 in my truck. Plugged the waterpump off and at an idle it ran 20 degrees hotter then with the bypass hose installed.