Have you contacted Oliver @ WeMoTec www.wemotec.com
to see if he can get you an HW-620 fan?
I would think the MidiFan is just a bit too big for it. Apart from the intake and outlet issue, it would leave very little place for the other components esp. the batteries.
Another option would be some other fan, in the 75mm to 85 mm range (the MiniFan makes no sense in the F-86 as it's too small a fan). In practice the possible choices would include the HW-620 (85mm), HW-609 (75mm), the DS 44 (85mm, pricy), or the Haoye fans about which I have no experience (do they wobble vibrate and fly apart as soon as you put a decent motor in them?).
Just for reference, my F-86 Sabre now flies with Springair 602's on ca. 1400 W with a Hacker B50 and 6S Flightpower evo 30C 3200's; I flew it three times this weekend and she's still a crowd pleaser. Low weight, low drag and good handling make it a fast plane.
In the pictures below I gave it a bit of armorall to bring out the shine after three years of flying