Upgrade 2040/3040 DOS 1 floppy drive to DOS 2?

Hello,

As the last remains of my PET retrivals, I have a handful of dual
floppy drives (3040 and 4040) in my basement. Up until today, I
thought they were all broken and were ready to throw them away.

However, I have just realized they're not broken - they are just
stuck with Commodore DOS 1.X as opposed to the 2.X versions I am
used to. Even the ones labelled 4040 have DOS 1 ROMs.

Now that I have good faith I can put together at least two or three
working floppy drives, I wonder if there is any way to upgrade them
to a newer DOS version. My EPROM programmer can handle 2532 chips,
so upgrading the ROM is not a problem, but I have noticed that a
DOS 2.x floppy drive uses a different 6530 RIOT than a DOS 1.

If I only upgrade ROM and keep the original RIOT, will it work at
all? Is there any custom DOS 2 compatible version that could be
made to run with a board otherwise equipped for DOS 1?

Is there some known replacement circuit for 6530 chips? I see there
exists BIN code from a DOS 2 chip, so I assume there is a way to
program an "emulation" as well. I do realize it contains RAM, I/O
and timers so not trivial.

If nothing else, I will continue to assemble and test my drives to
see how many I can get to work reliably, then see if anyone on the
list has spare RIOTs and perhaps ROMs too to trade with me.

Best regards

-- 
Anders Carlsson

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