The stock radiator does work ok if it is good shape...as well as the rest of the cooling system.
However, the stock radiators do tend to plug up over time with corrosion and deposits. This will effect the cooling system. Make sure your water pump is in good shape, as well as the cap, and T-stat, and also that you have bled the cooling system properly. I had an issue with hot temps my last year of IT with an 8-year old radiator. Car would run 190+ in cool weather. A new Modine OEM replacement dropped the temps right back to normal and it has run fine ever since.
I run a bone stock radiator on my G-Prod (limited prep motor but higher compression and more revs than IT) and ironically I have been fighting a problem getting the car to run hot enough!! I had issues with 150 degree water on a 95 degree day down at IRP two years ago. I tried substituting the T-stat with a simple plate with 5/8" hole but it ran too cold. I now carry two modified Stant brand T-stats that I switch between depending on the ambient temps i.e. run the 'hot' T-stat in cooler spring/fall weather and the 'cold' T-stat in the summer and use races tape to block off part of the grill to fine tune my temps. If you drill a series of small 1/8" holes in the outer perimeter and a 3/16" hole in place of the dribble pin, it will help drop your temps and make it easier to bleed as well. It will also take a little longer to warm up so you do need to plan ahead when you pull up to the false grid.
Make sure you shroud off the left side of the radiator to help keep the air from spilling off the side and forcing it thru the radiator. I use a scrp of air dam material about 2-3 inches wide cut to shape and bolted to the side if the radiator.
Removing the cooling fan is a compromise. The car will run cooler on the track since the stock fan actually blocks the airflow at speed, but you have to be careful idling the car or running in the paddock, and time when you start the engine relative to the 5-minute and 1-minute warning on the grid. I have been thinking about adding a small, light-weight aftermarket fan to help with this problem but presently I run without a fan.
Running plain water with Red Line Water Wetter will help with temps as well. Plain water is more efficient than anti-freeze. Use 'Steam' distilled water to minimize the deposits from minerals.
As Blake indicated, an oil cooler really helps these motors. Pegasus (and others) carry a real nice billet aluminum oil cooler adapter that sandwhiches between the block and the stock oil filter. This will allow you to plumb an aftermarket cooler. Use a good synthetic oil like redline/mobil1/amsoil etc.