Hmmm..........this thread is dear to my heart.......
I've had the Radtec and Pro-Alloy rads on a 2wd Cossie - turns out if you have a 4x4 i/c on a 2wd car ( can't comment on the 4x4 ) neither will fit "out the box" as the top of the rad butts up to the bottom of the cooler.

You need to replicate the top of the std 4x4 rad to make them fit.

All I can say is that the Pro-alloy one involves less cutting.

As has also been said, if you've got a 500-type i/c and are using the spare set of rad mounting holes you won't have to mod either the Radtec one or Pro-Alloy type at all.

As a footnote - anyone know if you can get alloy rads repaired if one of the cooling fins is fractured?