Radiator selection help.

I also have one of those radiators. I can't remember what size I have offhand but I went for the biggest I could fit between frame rails. I did also cut the opening to get the most air in also. Not a great thing if you want to retain the factory sheetmetal but that was not a worry after already cutting the fenderwells out for headers. I have had no problems with it at all. It works so good that I have to block off part of it when it's cold out or it won't warm up for quite a while.