Custom Dragon with Left-over APAS from STS, as ACRV?

[sdsds]

In theory, could an APAS docking system from one of the STS airlocks be attached to the CBM of a cargo Dragon? Would it fit under the nosecap? Did the use of SSRMS during STS-132 to "dock" MRM-1 demonstrate the capability to dock a Dragon outfitted with APAS at PMA-2? Could that Dragon then function as an assured crew return vehicle, thus providing (ahem) "redundancy" to Soyuz-based return for USOS flight crew?

[Zardar]

In theory, could an APAS docking system from one of the STS airlocks be attached to the CBM of a cargo Dragon? Would it fit under the nosecap? Did the use of SSRMS during STS-132 to "dock" MRM-1 demonstrate the capability to dock a Dragon outfitted with APAS at PMA-2? Could that Dragon then function as an assured crew return vehicle, thus providing (ahem) "redundancy" to Soyuz-based return for USOS flight crew?

No.

Leaving aside all the issues with the old hardware probably not still being available and flight-qualified, and the amount of  procedural/safety issues that would need to be developed and documented, (including making sure that the 'dragon apas" could be safely jettisoned in case of a problem) the STS orbiter airlock mods/extensions to implement and support the APAS hardware were probably far too big and heavy to fit onto dragon.

"Atlantis received extensive wiring changes to accommodate the new system, which measured nearly 15 feet wide, 6-˝ feet long, and 13-˝ feet high and weighed more than 3,500 pounds."

(From http://www.spacefacts.de/mission/english/sts-71.htm)

[sdsds]

In theory, could an APAS docking system from one of the STS airlocks be attached to the CBM of a cargo Dragon? Would it fit under the nosecap?

the STS orbiter airlock mods/extensions to implement and support the APAS hardware were probably far too big and heavy to fit onto dragon.

"Atlantis received extensive wiring changes to accommodate the new system, which measured nearly 15 feet wide, 6-˝ feet long, and 13-˝ feet high and weighed more than 3,500 pounds."

(From http://www.spacefacts.de/mission/english/sts-71.htm)

That's a description of the entire airlock! From that same page, "A 632-pound Russian-built docking mechanism, called the androgynous peripheral assembly system (APAS), [was] mounted on top of the airlock and docking base."

632 pounds (287 kg) is certainly big, but not that big. I agree that more mass would be required to mount the APAS hardware onto a CBM. A PMA sort of does this job, and they are fairly massive!

Regarding the availability of the STS airlock hardware: I'm pretty sure it is being carefully maintained, and that two sets are "available" for flight. The "Exploration Gateway Platform" proposal would have used one:
http://www.nasaspaceflight.com/2011/12/exploration-gateway-platform-hosting-reusable-lunar-lander-proposed/
http://www.nasa.gov/pdf/604659main_6%20-%20Panel%203_Raftery_Final.pdf