BASIC.SYSTEM replacement with DOS 3.3 i/o hook semantics?

[lyricalnanoha <lyricalnanoha@usotsuki.hoshinet.org>]

I'm getting back to this after some investigation allowed me to port some 
old MECC disks to ProDOS 8.  Some time ago I proposed the concept of a 
"DOS 3.3 to ProDOS port" and was advised that it would be unfeasible due 
to programs which pounded too hard on DOS 3.3 itself, but most of what 
I've been working with is mostly Applesoft, with a smattering of machine 
code, and the latter is what causes trouble on ProDOS with BASIC.SYSTEM. 
Often this is the fault of a chargen and sometimes a POKE 1002,96 will fix 
things.  In some cases, that isn't enough.

So I figured I'd want to try this again.  (I've never really "gotten" 
ProDOS though, even with Beneath Apple ProDOS, so :/)

In particular - the programs I want to port can be modified trivially to 
work around file access semantics, filename limitations, etc. - but the 
parts which crash BASIC.SYSTEM or cause it to malfunction can't be 
patched.  Necessarily this means the problem is related to differences 
between the structure of the two systems.  In some cases, e.g., if they do 
not need to rely on text files, it is fully possible with adjustments to 
run them on RDOS and also on PDOS.SYSTEM.  That doesn't help every case, 
however, so a BASIC.SYSTEM clone using the old DOS semantics is still 
desirable.

So far, the programs in question are Elementary Volume 7 by MECC, and 
Shifty Sam by Random House.  (Why? Why not!)

-uso.