Difference between manual and power steering couplers, all years
The only difference between a manual steering and power steering box coupler is the size of the splined hole. Manual steering coupler splined hole is approx .700" in dia. Power steering coupler splined hole is approx .600" in dia The length does NOT have anything to do with wether its for manual or power steering.

There were basically 4 different style steering column couplers for 62-93 vehicles. 

62-65 A & B body coupler has a split collar with a bolt to connect to splined shaft on steering box
There are no rebuild kits made specifically for these couplers. The newer 67-76 rebuild kits available from Mopar can be used except for the spring steel clip that helps spread the shoes inside the coupler. That piece is different between the early and late couplers.

66 A & B body coupler has a split collar with a roll pin to connect to splined shaft on steering box
There are no rebuild kits made specifically for these couplers. The newer 67-76 rebuild kits available from Mopar can be used except for the spring steel clip that helps spread the shoes inside the coupler. That piece is different between the early and late couplers.

3" couplers were used on;
All 66-73 models except 66 A bodies that used a very different early style coupler and 73-74 B bodies that used the 3-1/2" coupler. 

3-1/2" couplers were used on;
74-76 A Bodies - Dart, Dart Sport, Duster, Swinger, Valiant
75-79 B Bodies - Roadrunner, Fury, Monaco, Magnum
74 E Bodies - Barracuda, Challenger
76-80 F Bodies - Aspen, Volare
77-89 M Bodies - Diplomat, Lebaron, Fifth Ave, New Yorker
87-93 Dodge D & W Series Trucks
87-93 Dodge B Series Vans

Coupler part numbers
1974-up 3748267 3-1/2" Manual, 3748268 3-1/2" Power 

1973 3420152 3" Manual, 3420153 3" Power (these part numbers superceded 66-72 numbers below)

1966-1972 2800705, 2996856, 3420152, 3579521 3" Manual, 2800706, 2996857, 3420153, 3579522 3" Power

More coupler related part numbers
2800741 Rubber seal (62-93)

2530538 66-93 Steering Coupler Cover