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my goal is to extract these coins into electrum without ever going online.
For the keys, you can export them from Bitcoin Core without going online, do what I've said in my previous reply but in the offline device.
Bitcoin Core's P2SH addresses are actually P2SH-SegWit unlike Armory's P2SH-P2PK, Electrum supports them,
just add p2wpkh-p2sh: before the private key, importing it to an offline Electrum wont allow you to spend and wont have an updated balance.
If you decided to create a Cold Storage set-up, you can "sweep" the key(s) (Wallet->Private keys->Sweep) to the online watch-only Electrum that's paired to the offline Electrum.
That will create a transaction that spends its entire balance to one of the wallet's address.
You can spend from it by following the last few info of the "cold storage" tutorial link: create-an-unsigned-transaction, except the latest version's save is named "export".