Jut wondering the concensus out there on this, I would think a 3:36 would be better for a 253 running an M20 box, due to the better first gear ratio, 3:08 if you are running the M21 and want top speed. My Ute is running M20/3:08 combination and 1st gear is pretty sluggish and I would like to change to a 3:36, I am not interested in top end as it will be a weekend cruiser only and it is the original specification. One web site lists the 3:36 diff as the performance option for the 253/M20 combination. (M20 has 3.05;1 ratio 1st gear compared to 2.54:1 in the M21)