Can I use 3 core radiator with the stock fan and shroud?

I think it depends on the 3-core radiator that you have. Get out the tape measure and start measuring the differences between the stock radiator and the new one. Then you can figure out if it'll work.

Or, since you already have the front end apart, just go ahead and dry-fit the new radiator with the stock fan and shroud, and see if it fits.

The 3-core I have was designed to fit the stock radiator mounts. Overall, it's a little wider than stock and moves the shroud back about 3/4". There is no interference with the fan, but moving the shroud back like that slightly reduces the fan's efficiency. The extra cooling provided by the radiator more than makes up for it, though.

I have a Ron Davis aluminum 3 core radiator and I tried the stock fan for a few weeks but the car would overheat with the A/C on when I got stuck in traffic in Dallas. This would only happen if it was 90* + outside.

I have since upgraded to a MK8 fan and a Delta Current Controller and have been pleased with the results.

The Taurus fan should do fine too...