From Spaced Ranger's analysis above, it looks like the cropping has extended the actual aspect ratio to around 2.75:1.
Therefore, the AviSynth resize step, assuming you are encoding in 16:9 anamorphic (why wouldn't you?) would be:
Spline36Resize(720, 310)
AddBorders(0, 85, 0, 85)
Yes AviSynth does have other resizing algorithms; you could try lanczosresize or lanczos4resize which are supposed to be sharper with a higher risk of artefacts, but to be honest I don't think there'd be any noticable difference.
Your raw frame would look like this:
And when played back on a 16:9 display, it would look something like this:
