Requirements: FULLY synced Bitcoin Gold Core (needs to be fully synced so that it detects that SegWit has been activated) that IS NOT "pruned" (so you can -rescan)
Step 1 - Get your private key data from block.io, this will be in the form:
* Address Type: P2WSH-over-P2SH
* Required Signatures: 2
* Redeem Script: 2 035fdaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaadedf1 029c7bbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbb90d92 OP_CHECKMULTISIG
* Redeem Script Hex: 522xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx2ae
* Public Keys: ["035fdaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaadedf1", "029c7bbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbb90d9"]
* Private Keys: ["L4nSdddddddddddddddddddddddddddddddddddddddddBZ", "L32eeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeaE"]
* Complete. Handle with secrecy. Do not share. Do not store insecurely.
Step 2 - In Bitcoin Gold Core, import the two private keys that you got from block.io
In the Debug Console (Help -> Debug Window -> Console), use the following commands:
importprivkey "L4nSdddddddddddddddddddddddddddddddddddddddddBZ" "" false
importprivkey "L32eeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeaE" "" false
Step 3 - In Bitcoin Gold Core, create the "legacy" multisig for the addresses you just imported, by using "Public Keys"
In the Debug Console, use the following command:
addmultisigaddress 2 '["035fdaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaadedf1", "029c7bbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbb90d9"]'
This will output the "Legacy" Multisig Address like: GGtN2fhfhgfhgfhgfhgfgfhgfhfghMASB
Step 4 - In Bitcoin Gold Core, create the "SegWit" address for the multisig address you just created
In debug console:
addwitnessaddress "GGtN2fhfhgfhgfhgfhgfgfhgfhfghMASB"
This will output the "SegWit" Multisig Address like: AHsv5kad3716AoHqmjzg3yaynVZLV7yuxN
NOTE: You can confirm you have done it successfully, by copy/pasting the "3"-Address from block.io into https://btgexplorer.com/ It will automatically convert the BTC address to the BTG one:
Once you have successfully created the "A"-Address in Bitcoin Gold Core, you need to shut it down, and restart it with the -rescan parameter. Then after waiting for it to rescan the blockchain, you should find all your BTG showing. You can then just send coins as you normally would with the Bitcoin Gold Core GUI and send all the BTG to the BTG address of your choice.
PROTIP: If you have multiple addresses from block.io, I'd recommend recreating them ALL in Bitcoin Gold Core first BEFORE you do the -rescan... as -rescan takes a LONG time
That's really usefull