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The HA feature is supported when you use the same versions on both nodes, and I don't know whether a 32/64 HA pair has been validated. I would definitely recommend using the 64-bit for both nodes.
If you are ultimately looking to migrate from 32-bit to 64-bit, and not to use HA long term, you can do a full database backup and restore to the new HM. You will have to call support so they can transfer your licensing over to new server.