Glad to see you found a way to do it that worked for you too. The cooler I had is identical to your cooler, and about half the size so will likely only marginally cool the fluid, but it was 'free' and it will help this Trans live longer, I think.
I didn't want to restrict the air flow or create turbulence across the condenser or rad, so I elected
not to add mounts at all.
Like you, I also didn't want it to rub on the condenser (due to road vibrations) so I bolted the cooler to the lower transverse rad support. There is a two to three inch air gap between it and the condenser. It gets plenty of air from the road.
Of interest is this link I found that describes the installation of a cooler on a GP.
http://www.grandprix.net/upgrades/cooler.html
What got me thinking is the routing of the hot fluid through the cooler on the rad. My logic tells me that the hot fluid should enter the top of the rad and fall while being cooled by the anti freeze toward
the bottom of the rad, exiting at least a few degrees cooler.
But the article contradicts this, suggesting that the cooler fluid exits
the top of the rad. If this is correct, I have to grab the other line returning from the rad and route through the cooler. I've sent an inquiry to the fellow who wrote the article asking for his clarification and will post once received.