What year 261? Some of the suggestions below are different for different years.
-Water pump adapter plate - Yes, and a 1952 water pump
-It has a 12v generator so new regulator - Yes (and a ballast resister)
-Bellhousing? Do I use the 216's? - Yes (and, you might have to modify the front plate on the block for the front motor mount)
-flywheel? - use the 261's flywheel (12v starter?)
-Clutch? - use the 261's set
-Accelerator modification? - most likely. You should be able to use the bell-crank and up-rod to the carburetor; however, the pedal to bell-crank rod might have to be shortened.
Tim
