You really should add timestamping to ArchiveBox. The easiest way to do that would be via my OpenTimestamps protocol,
https://opentimestamps.org It's open source and free to use, and uses Bitcoin for the actual timestamps. Users of it do
not need to make Bitcoin transactions themselves as a set of community calendar servers do that for you. You also don't need a Bitcoin node to create an OTS timestamp, and you can validate an OTS timestamp without a Bitcoin node as well by trusting someone else to do that for you.
The big thing that ArchiveBox can't do, and the Internet Archive can, is attest to the accuracy of the archive. Being at least able to prove that the archive was created in the past, prior to there being a reason to tamper it, is the best we can realistically do with current cryptography. So it'd be really good if support for timestamping was added.
IIUC ArchiveBox is written in Python; OTS has a Python library that should work fine for you: https://github.com/opentimestamps/python-opentimestamps