Measure five times, question your measurement, have your wife come out and check your measurements another four times, argue a little bit, measure three more times and then cut :grin2:Nice work. I'm probably going to be doing the mod on the front end of my car for a 24" radiator. Any tips you can pass along from doing it on your car?
I found the center of the radiator and then measure out to the edge of the air portion. Then I did the same measurement on the car and marked with chalk in the center, top, and bottom. I then measured diagonally from the top corners to the bottom corners to make sure they were both equal. Use a known straight edge (like a level) to finish drawing out your lines. Check the measurements from top and bottom as well as side to side again at every point. When satisfied...measure again. When you're sure you have it right...measure one more time. After everything is certain let the cutting being. Cut the inside of the line. I used a plasma cutter but a cutoff wheel or body saw would also do the trick. Take your time cause it's real hard to get a do-over on this. After you're done cutting, smooth out any rough edges.
For the radiator, this one has dowels welded in the bottom that sit down into the frame rail. I used white out on the bottoms of the dowls to find the drill point. From there drill a small pilot hole and then work your way up to the proper size. Sit the radiator down in to verify everything's cool and go pour some whiskey.
Quick word of caution...dont set the radiator flat against the support when you get ready to do your holes. I did that and noticed it didnt want to sit the in the opening very well. Setting it back about 1/4-3/8 inch did the trick.