This is the 81-88 top mount Bracket for the taller version:
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This fits the replacement 20-1/2" x 28" core.
They also sold a 17" core using different core support holes:
The plate pictured above by ParieDrifter is 73-80 only?
I wanted to install one but could not confirm it would work on the 87' Blazer core support.
Be great if it it fits because the plastic spacer is weak.
These are for the 81-88 17" core:
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These mount on the inside of the same core support used for the 20-1/2" radiator, only these fit the 17" tall radiator.
If you look closely on the OEM core support, you will see there is bolt holes for either size radiator.
Naturally the shroud is very different.
If you are going to go aftermarket radiator, sometimes going thicker and shorter allows you to use these lower bolt holes to fabricate easier, than trying to split hairs with the top mount style brackets listed first.
When you lower the radiator below the top of the core support, such as the 17" cores, you also remove part of the "seat" for working on the engine and the chance your weight will bend and cause a leak in the taller radiator. The shorter radiator, with a custom shroud and electric fans has it's advantages, so long as you account for the heat load with A/C.