The 3-row radiator for the '65 Mustang is an easy way to upgrade your cooling system. It is exactly like the stock Comet 2-row radiator in every way except that it is about a 1/2" thicker. This puts it dangerously close to the fan in the stock location. The easy solution is to move it back into the radiator support.
From this distance the modification looks stock.
Where the silver bolt heads are is where the radiator flange normally sits. Instead I have made a cut at the top of where the radiator support bows out and slid the flange down inside the support. You'll need to make this cut on both sides, and another smaller cut at the bottoms to get it to drop in and line up. the cuts have to be a bit wider than the thickness of the flange to accommodate where the flange has some stiffening bends.
My original mounting clips & bolts were in sad shape, so I used all new nuts & bolts. If you feed them from the engine side forward you don't have to worry about them interfering with anything in the engine compartment. (those hoses are for an external transmission cooler)