I had space issues with my 48 and originally went the route out a cheap pusher fan of Ebay. I soon learned I had cooling issues. I went with a Cooling Components puller fan. Here is their site:
http://coolingcomponentsinc.us.com
One of their fans is 2 5/8" thick and comes with a housing you can trim to fit. They also offer a two speed switch and they move some CFM's. They are not cheap but very effective.
After talking with them they also suggested not using the (convenient) flex radiator hoses. The corrugated surface of the hoses causes turbulence on the inside of the hoses which effects your coolant flow rate. Once I changed my hoses (I went with bend pipe for hoses) and my fan I no longer had any cooling issues. I should mention that I did notch the core support to push the radiator as far forward as I could to clear to gain every inch I could.
Good luck
Marc