First off, cut the opening to support a bigger rad...Its not sacrilidge, its just more air flow.

Two, when it comes to radiators, you get what you pay for. The guys that say, works fine for me, may not always work for you. Radiators range in price from $160-$1000, and there is a reason. Some cool better than others.

When shopping for one, call up the vendor and get an idea on how much HP its rated for...I went thru a few on my one car, and it can be a big pain in the a$$ to do it twice. Finally ended up with a Becool rated for lots of HP and have never had a problem since. Its also a $700 radiator...I recommend BeCool or Affco rads as some of the better ones. Call them, and find out more.