Use a fine file or some fine sandpaper (emery cloth) to smooth up the studs on the arms/bearing caps to let them slide into the bearings easily. No problem with flat spotting them, just do a little sanding (grab the stud in between finger/thumb with sandpaper wrapped around, spin the stud), then check the fit and repeat as needed. You'll soon be able to find the high spots on the stud and be able to knock them down.

Fish scale is easy, just attach the hook and pull until the knuckle moves, watch force on scale. Do test with both bearings installed and tight and the rubber/felt wipers on the back *not* attached.