[Joe Gavin]

That math is little weird with the 4:3 ratio but got a simple trick … Wanna keep the height & crop wide… This ratio works like this. In any 16:9 sequence 720 to 8k footage. Just keep 75% of the width pixles…
Step 1( place a black color matte your sequence ratio in timeline) Step 2 ( place a white color matte over the black same same) Step 3 (Put crop effect on white color matte 12.5% on Left and12.5% on Right) BOOM 4:3 ratio… Step 4 (Nest black and white matte) Step 5 ( set nested clip opacity to darken) POW done
At Export Time 0.75×Width = New Width