62 Valiant rear

Standard-equipment ratios in '62 were 3.55 with manual trans and 170 engine, 3.23 with manual trans and 225 engine, 3.23 with auto trans and 170 engine, 3.23 with auto trans and 225 engine (early production), 2.93 with auto trans and 225 engine (late production).

Any 7¼" rear axle assembly from any A-body through '72 will drop directly into your '62, as will one from a '73-up A-body with the small 4" wheel bolt pattern (most '73-'76 A-bodies have the larger 4½" bolt circle).

Most common ratio '63-'68 is 2.93 with automatic, 3.23 with manual.
Most common ratio '69-up is 2.76 with automatic, 3.23 with manual.

Pick your rear axle ratio according to what engine you have, what kind of driving you do and whether you prioritize easy highway cruising and good fuel economy (numerically lower ratio like 2.93 or 2.76) or quick acceleration around town (numerically higher ratio like 3.23). If you change ratio from what you have now, you will need to change the speedometer drive pinion so your speedometer reads correctly.