That was one of the earlier swap in's I did with my 64 CDV. Did not come with it, but early parts car had it. I would guess about 1 in 5 of the 49 parts / 5 driver 1963/64's I have had on hand had the optional controlled differential. I think almost all were G1's... the 3.21 gear ratio and do not recall a G2 for the 2.94 rear end ratio.
I have a controlled 2.94 gearset in mine. Came stock.
I have a controlled diff. in a parts car. What would I benefit from making the swap?
Better Traction in compromising situations such as snow, sand, or mud where the pulling tire might slip. On a regular Hypoid differential power is sent to wheel with least traction. That is why if you get one rear tire off the ground, or in snow or mud, etc, it will just spin. Controlled differentials send turning power to wheel with more traction. If you are an old poor hot rodder like me, and cannot afford an expensive "locker" rear end, you can use a Posi rear end, on level pavement to pull from both wheels and do those 2 wheel burnouts. When I first installed my posi rear end I headed to a parking lot across the street, held the brakes and did a 2 wheel fish tail burnout... just enough to rekindle the days at the drag strip! LOL
For regular dry payment road use it is not going to make that much difference, other than the comfort of knowing that if you had to go off on the shoulder of the road or onto a compromising situation you had better traction.
Is the ratio close enough not to notice an rpm difference?
You should have a slight difference in the speedometer reading unless yiu change the gear in the trans
You can check your speed difference between your speedo reading and -the speedometer GPS app --on your smart phone
Good to use if the spreedometer has any issues at all ( as in not working correctly )