don't forget to check the hight of a radiator when looking at the wreckers etc.. some are too tall.
s13 radiator is alloy, single core and just fits, not much clearance with the bonnet. that model excel rad it twin core. i went to a korean wreckers locally, and asked for that very radiator i believed it was from an X3 (?) and it was single core, he said he didnt know of any excel radiators that thee anything but.
you can also use a radiator with outlets on the wrong side, ive seen someone use 2 rubber elbows and a peice of stainless, also seen someone use a long flexable pipe, it from a u13 sr20det bluebird into a 4age ke70. its better to have the outlets on the correct side but its not essential. but as has already been said there are heaps of options, just as long as they fit. the tech-art (spelling) N2 86 (probaly about the highest budget and most competitive) uses a radiator from a tractor!