If I were doing a FWI like yourse, I would use:
Throttlebody > 3" to 4" adapter > 4" bend> 4" to 3" adapter > MAF > 3" to 4" adapter > 4" straight pipe > 4" adapter > 4" bend > 4"-opening filter
Optimally all bends should be 4". A 4" 90* bend has roughly the same properties as 3" straight pipe. Obviously, the ~22.5* bend off the throttlebody and the 45* (is that 45*?) bend at the filter only equal 67.5* total bend, but there's no reason to do anything but 4".