This is how I did mine,,using a ruler or tape measure,center the wing on the trunk lid.Use masking tape to protect the finish on the car and double check that the wing is centered by measuring the left and right side distance from the side edge of the trunk lid..
To find the rear mounting hole locations on both sides you have to measure on a 70 to 71 challenger measure from the bottom edge of the trunk lid forward,following the contour of the trunk lid 8-1/2" which is to the back of the spoiler leg rear stud,,,on a 70 cuda measure from break line(not bottom edge) on the trunk lid forward ,following the contour of the trunk lid 5-7/16" on the 71 cuda it is 8-1/8" to the back of the spoiler leg rear stud..
Using the spoiler leg studs as a guide,find the forward mounting hole locations (measure the distance between the 2 studs on the spoiler leg and transfer that measurement forward from the rear mounting hole location) then drill 4 mounting holes 5/16" and mount the spoiler legs and gaskets and spoiler,,this is how its outlined in a yearone catalog and when you have that done you can figure out were the braces under the trunk mount and were to drill the holes,,I used u-nuts after I drilled the holes and secured the braces with bolts to the u-nuts,,if you can get a yearone catalog it has a small picture and these instructions,it was very helpful when I installed mine,,and was the only reference I had and mine turned out perfect,,you should find the catalog if your unsure as I know when its once drilled its permanent
