I used "well nuts" ( I think that's what they are called?) My local industrial hardware supply has a huge box of them and they were just the thing I needed when I was mounting my Allstar rad. If anyone needs some and can't find them locally I can see if they still have some? I think they were 3 bucks each or something like that?
"Well nuts"
Then I made a small bracket and used stainless carriage bolts with a small flat milled on the side so you can get a wrench on it so it won't spin when I used stainless nylon lock nut and stainless washers on the other side. This mounted it in rubber so it will take some shock. I didn't want to mount it solid. I then just pop riveted it to the flange on the rad ( top off rad) 4 rivets per bracket. It does go around the back side of the flange( U shaped) ,just can't see it very good in the picture?
On the bottom I went to the junkyard and found some of these stock rubber mounts for rads ( I think it was for a ford truck but can't remember?) My local junkyard removes all the rads so I could see these sitting in the bottom on the rad saddles in the cars. I took a few pairs in different sizes. I got a pair that fits snug in the flange that is on the rad on the bottom.
I then milled slots that snugly fit the rubber mounts in a flat plate that uses the holes to attach to the car that are already there on the rad support. I also added a support from under the rad to support to the new plate I just added. I had to drill those holes though.