Big Bird and co will NOT be playable without some crashes as I found mislabeled loadouts.
Nothing wrong with getting the script, Atoka, the more have it and publish converted campaigns, the better
But it takes some getting used to and some planning to convert a campaign. What replaces what and how to do it (mass search and replace) requires care and it gets better with experience. So tinker with it and test what you do for yourself first. Check maps too, which the tool can't. Maybe a map name is spelled differently and needs fixing, some maps have been altered by modders over the years and some layouts have changed so airfields and ports can be moved. Things like that...
I already have a sheet of standard typical replacement actions from a long time doing this, so for this one, I'd offer to convert the mis files to include only available objects and you can then improve them with FMB.
It looks like Boxcar is basically a plane replacement set of files, so I will do that as well in one go.
As for contacting the maker... JS was last active in 2012-ish. Most likely you won't catch the man anyway. Don't let this roadblock you.
PS:
here is the modified package of Big Bird and Boxcar
https://www.mediafire.com/file/eq1j180uzinrftd/Big_Bird_and_Boxcar.zip/file