A "shortcut" would be to simply run PyWallet recovery across the disk that possibly had the wallet.dat on it... if there is a "recoverable" wallet file or key data, it should find it.
You can read more here:
https://bitcointalk.org/index.php?topic=34028.0The instructions for recover is here:
https://bitcointalk.org/index.php?topic=38004.0However, if the drive has been formatted/re-used, your chances of recovery are not great. You should probably also consider making an image of the drive, rather than working directly on the drive to prevent any further accidental data loss.
If it was blockchain.info, you're probably not going to find anything useful in recovered files... the system stores your encrypted wallet on blockchain.info servers... you need your wallet ID and password to be able to download and decrypt the file.
... I do remember using Blockchain.info to check a few times (2011).
... I do remember is that he had to download the entire blockchain to his laptop before he set up my account.
... I do remember setting up a password and re-typing a seed with randomly generated words (can't find).
... Was the SMS confirmation available at this time as well? I vaguely remember doing this but could be wrong.
Honestly, you seem to have "remembered" pretty much all the various features of all the various bitcoin wallets
downloading blockchain = Core, using blockchain.info, SMS auth, using a seed mnemonic etc...
If you used a recovery seed mnemonic, then it most likely won't be a wallet.dat... and it isn't likely to be a Bitcoin Core (aka BitcoinQt) wallet.dat file that you're looking for. Although newer versions of Bitcoin Core are "HD" and derive addresses from "seeds" they have never used BIP39 backup seed mnemonics. Bitcoin Core has always relied on making backups of the wallet.dat for recovery purporses.
Given you have no idea what wallet or format your wallet and/or private keys were being stored in, you effectively have no idea what you're looking for, so your chances of being able to identify anything recovered from that drive a pretty slim.
You're looking for an unknown object in a stack of (most likely corrupted) objects