Looking for input/suggestions about rear end changes

"Calculator"? It's just a ratio. At 55 mph, engine revs with the 3.55 gears will be 3.55/3.73 of the revs with the 3.73 gears. That's 95%.

If you are unfamiliar with rearend and gear changes, my suggestion is to have a rearend guy do it. Knowing what set-up fits what housing and shimming is critical and you don't want to buy the parts twice.

John, I had 3.55's in my first 65, with an M-21, it ran like a scalded dog but I launched hard, at drove at high RPM and shifted at six grand to make it move. 3.55's will give you a comfortable cruise, 3.73's and lower gears will create noise and fuel economy issues for a road car but are better for the "stoplight Grand Prix". Totally agree it is a job for a professional, and you need to do everything from drum to drum while it is apart. Brakes, axle seals and bearings, carrier bearings, everything. Any old parts like wheel bearings will most certainly fail under the stress from new, strong lower gears and posi, because you are going to thrash it when you have the new found power! I easily destroyed the GM posi units (Auburn) on the street. I am going to install a Detroit Locker this time around. You are looking at $400 to $500 in labor, so put in the best parts to avoid re-do labor cost. I would source all the parts from Summit or Jeg's, because they will make sure you get all the proper parts matches, and warranty is really easy if there is any problem. Jeg's will price match any part, find the cheapest price anywhere and call them. No freight or Sales Tax for us here in Florida when you buy from them either. One more thing, tire size is important. If your tires are less than 27", the stock diameter, you will slow the car down.

with the close ratio trans i would go with 3.73s ,if you don't like it a taller tire would make up the difference.26.5 is a fairly short tire.my .02 jc