Yes for Bitcoin, No for gold. Roughly...

1) Unless you already manage the 401k, quit that job to allow for a rollover

2) Start your own company. Ideally an LLC

3) Work with a service like solo401k.com to setup your 401k plan for the company.

4) Open accounts under the plan as needed for usd funds, exchanges, and collaborative multisig (e.g. unchained). These are indepent of banking accounts you opened for the business itself.

5) Roll the funds over from old employer plan to your new plan

6) Transfer funds to exchange account to buy bitcoin

7) Withdraw the bitcoin into the multisig account.

DIY research. Not Financial Advice

solo401k.com

unchained.com

https://unchained.com/blog/ultimate-guide-to-bitcoin-retirement-savings/