you already have a puller type fan, what Im suggesting is to get rid of the original fan motor, blade and shroud and install a good fan in place. SPAL is a good choice here - You can get creative and use the original shroud.
The puller means it pulls air through. - Do not try to reverse polarity of a pusher to make a puller.
For cleaning - 400 grams of citric acid crystals to 4 litre water will do a very good job of cleanup. Be sure to flush the system thoroughly before and after this treatment. neutralize with meetha soda, flush again, check for leaks and fill with coolant.