When mounting in the attic I generally use a larger antenna than the basic report would suggest for unobstructed outdoor mounting. Another consideration is the ability to refold or otherwise remove the antenna from the attic.
So, in this case I'd suggest using the largest 'All-Channel' antenna that will fit in the space while being pointed toward Chicago. Antennacraft is fairly easy to refold.
http://www.antennacraft.net/Antennas...llChannel.html
Re. your question, "... do you believe that I could get acceptable signal strength with an attic install?", ultimately, you need to put an antenna up there and see. Many folks do great, but the building materials play a big role. Metal roofing, foil faced insulation, duct-work, etc. are signal blocker/reflectors.