Gary, I know you also posted this question on GMF. To save time, I will respond here on TS, and add a link to your GMF post.
The information for the mid wing location was measured from my stock Canadian market 1991 Chevrolet Sprint Turbo hatch.
General: The mid wing spoiler is secured to the hatch with a total of 4 Phillips pan head bolts. (2 per side).
This photo shows the location of one of the 2 upper pan head bolts. The hatch sheet metal is double walled here, so an access hole of 3/4"diameter is needed to allow access for the upper mid wing bolts to pass through the exterior sheet metal to the mid wing spoiler. The round factory black plastic tape cover has been peeled back in this photo to show the upper bolt and access hole.

The 2 lower bolts go directly through the sheet metal to the mid wing, and use a fender washer.

Below is a picture view of the upper and lower bolts attached to the mid wing. The upper bolt is covered by a round black factory tape over the 3/4 inch access hole.

Next below, is a picture of the hatch of a Swift without the mid wing. This example has a GT upper hatch spoiler. Note there are no holes pre-drilled for an owner to simply bolt on a mid wing spoiler later on - for cars without a mid wing spoiler from the factory.
I have added several reference points to the hatch (marked in
red) to allow one to locate where to drill the upper and lower mounting bolt holes on each side of the hatch door, to be drilled from the inside of the hatch door outward through the external sheet metal. You can use a smaller drill bit first so you can check that the mid wing holes line up properly before drilling full size holes.
You may need to zoom in on the photo to see the
red letter reference symbols better:
X= bottom edge of hatch door sheet metal (at end of an imaginary line passing through centres of L, X, Y)
Y= upper edge of holes in sheet metal where the black adjustable rubber hatch bumpers are screwed in.
Z= centre point of the black plastic plugs located under the upper hatch door hinges.
U= location of the centre point of the upper mid wing bolts.
L= location of the centre point of the lower mid wing bolts.
Distances and measurements:X to L = 7.25 inches
U to Z = 16.75 inches (centre to centre)
U TO L = 6.50 inches (bolt centres)
L TO Y = 4.00 inches (bolt centre to edge of hole)
U to edge of black hatch trim adjacent to hatch window = 1.50 inches (bolt centre to edge)
L to edge of black hatch trim adjacent to hatch window = 1.50 inches (bolt centre to edge)
