From the API 250 General Pistol Course student handbook, circa 1988...
Auto Pistol Modification Table
Necessary
High Visibility Sights (including ramped front)
Dehorning (rounding all sharp corners)
A good trigger (3 1/2 to 4 1/2 pounds, crisp)
Useful
Solid Bushing
Enlarged Ejection Port
Beveled Magazine Well
Extended Thumb Safety
Throated Barrel and Polished Feed Ramp
Round and Polish Bottom of Extractor Hook
Press Fit of Firing Pin Stop
Lanyard Loop
OK
Magazine Floor Plate Pads
Colored Sights
Flat Mainspring Housing
Spring Modification to Magazine Release
Accuracy (Combat Accuracy Job - slight tightening of slide, solid bushing without being tight, fit of barrel hood, link and slide stop to barrel lugs - 3 to 5 inches at 50 yards.)
Questionable
Duck Tail Grip Safety
Ambidextrous Thumb Safety (necessary for left-handed shooters)
Custom Stocks
Stainless Steel Parts
Recoil Buffer
Trigger Stop ( for over-travel)
Objectionable
Sight Rib
Optical Sights
Trigger Shoe
Extended Slide Stop
Squared or Hooked Trigger Guard
Loaded Chamber Indicator
Double-Action Conversion
Muzzle Brake
Over-length Barrel
Extended Magazine Release
Recoil Spring Guide Rod
Long Slide
Group Gripper
Ejector Modified to Drop Brass Close
Accuracy (Maximum Accuracy Job - 1 3/4 to 2 1/2 inches at 50 yards, hard fit and lapping, maximum tightness, etc.