The basics of this adjustment are:
Attach the levers to the transmission and shift them to neutral.
Attach the mechanism to the tailshaft housing, different position for Nova (two spacers required) Chevelle (no extra parts required) and Impala (mounting plate required). Use a gauge to position the mechanism into neutral and keep it there.
Adjust rods to fit this neutral position. Tighten everything up and test the shifting.

Below is the procedure as it relates to the diagram. You will find this procedure in any GM shop manual for 64-67.

1. Attach the transmission levers (M),(P)and(S) to the transmission and set to neutral. Attach shifter mechanism to tail shaft housing.
2. Move shifter (A) to neutral position and insert locating gauge (B) in control lever  bracket assembly slot. NOTE: make your own gauge. dimensions are 1/8 inch thick x 41/64  inches wide (0.646) x 3 inches long.
3. Install rod (V) with clip on lever (D), this is the 1-2 rod.
4. Maintaining lever (D) against locating gauge, adjust clevis(T) at lever (S) until clevis  pin freely passes through holes in clevis and lever.
5. Install clevis pin, and cotter pin, there may be a washer here as well.
6. Install rod (H) with retainer on lever (W). this is the reverse rod.
7. With jam nuts (J) and (L) and swivel (K) loose on the rod (H) insert and attach swivel  with washer and clip to lever (M).
8. Maintaining lever (W) against locating gauge (B)  Then tighten jam nut (L) against  swivel.
9.Install rod (R) with clip on lever (P).
10. With jam nuts (E) and (G) and swivel (F) loose on the rod (R), insert and attach swivel  with clip to lever (C).
11. Maintaining lever (C) against locating gauge (B), and while holding swivel (F), run jam  nut (G) against swivel until nut contacts swivel. Then tighten jam nut (E) against swivel.
12.Remove locating gauge and check shifts to ensure proper operation. Readjust clevis and  swivels if necessary.

NOTE: Control rods may be attached to transmission shift lever lower holes to reduce shift  lever travel, for a 'faster shift' adjustment option (1966-1967). Increased shifting effort  is required when control rods are installed in this 'short throw' position.