Also, afaik some games had bugs in their original DOS versions that have been fixed/worked around in ScummVM.
Also, it's more or less easy to just use the SDL backend/windows fs and port it to DOS. You could, for example, just write some SDL interface-compatible wrappers around the Allegro (or some other lib) functions, and try to keep as much of the SDL backend untouched. You'd be more or less implementing a small subset of SDL for DOS
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