Good Question?
Take a peek at Mikes site,for I-71 or I -72.Also,take off the muffler and measure the bore.I-71,I-72 is 2.125,with a 1.5 stroke ,795 is 2.217,with a 1.635 stroke 797 is 2.28 with a 1.835 stroke 840 is 2.165 with a 1.635 stroke 890 is 2.217 with a 1.635 stroke.The plot indeed thickens,the puzzle is not solved yet.