ANSWER: The IRS and 401k regulations do not allow for the deposit/transfer of 401k trusts, which fall under the retirement trust umbrella, to a living trust. However, a living trust, while it may not always be beneficial, may be named as the 401k primary or contingent beneficiary of a solo 401k.
Tarakan in Massachusetts
Solo 401k beneficiary distribution rules
Ed Slott's take on naming a living trust as a beneficiary of a solo 401k or IRA
What is a solo 401k trust?