I pulled the Optronics Sealed 4 Inch Round Trailer Light, # ST47RB, from the warehouse and measured the diameter of the light housing that will be recessed in the trailer. It measures 4.44 inches in diameter so a 4-1/2 inch hole should be fine.
I spoke with my contact at Optronics and they do not recommend a specific hole diameter for this light, but most flange and flush mounted 4 inch lights require a 4-1/2 inch diameter hole. view full answer...
According to the install instructions for the Curt hitch part # C13235 (that are attached), the horizontal mounting bracket of the Curt hitch part # C13235 does have the notch like our product pictures. I can assure you the hitch you order will have it and it will fit your 1999 Isuzu Amigo.
If you wanted to do some towing you might be interested in etrailer ball mount kit # 989900. It comes with 2 ball mounts; one with a 3/4 inch rise or 2 inch drop and one with a 2-3/4 inch rise or 4... view full answer...