I can't speak for the entire dev community but I, and I imagine nearly all the regulars, have a large archive of INVCOM versions going waaaay back. Tag someone to help; paid work of course.
You'll have a dance of upgrading to 4.2 (that's where I would start), and then 4.5, then you'll need to make server adjustments for PHP requirements, possibly before the 4.5 upgrade, then you'll be clear.
A slog, but a small one.