Unexpected Clearance Issue

the fan I purchased is a single fan. I sent ChallengerGary, the champion rep, an email and he responded right away. He said I can put the fan I bought on the front and just reverse polarity. I may try that but first I am going to see what size fans I could fit with the offset that "hotlines" spoke of. I prefer the fans to pullif possible but it might not be possible.
Rod