I started by selecting which two front/back halves seemed to fit together best, which ain't saying much because they don't fit well at all. However, two pairs did seem to go together better leaving less sanding/fit work. I assigned them their "left"/"right" labels and started marking, trimming, and sanding until the fit was great.
I then marked drill points on the flanges, mated them, and drilled #30 pilot holes through the flanges so that they'll go together.
