Thanks, that is helpful. I also subsequently realized that the situation I described is actually an application of the Mega Back Door Roth strategy (although a very small one in this case) - although I had not thought of it that way. And the link below provides further guidance on that (for anyone who might be interested). The trick will be working with the Solo 401 K Plan Administrator to property track the After Tax Money (i.e. the Profit Sharing Contributions made by the Sole Proprietor which were not claimed as Personal Deductions) in the Tradition 401 K Account, or alternately to correct this on the 1099-R which they issue for the subsequent Roth Conversion (if they fail to do so). The SECURE Act 2.0 also now allows Profit Sharing Contributions directly to the the Roth 401 K Account (beginning in 2023) so hopefully this will all be mute soon (i.e. after the Solo 401 K Plan Rules are modified accordingly). https://thefinancebuff.com/mega-backdoor-roth-in-turbotax.html#htoc-a
