Using funds from SD401K With Other Funds?

[Carlos Simmons]

Let's say I have $50K in my self directed 401K and $50 in cash to invest.  What would be the best way of:

a)  Purchasing a property for $100K

b)  Purchasing a note for $100K

c)  Buying a property to flip for $75K and put $25K into repairs

Can I use personal and 401K funds in the same investment as long as there is a clear distinction between the two?  For instance, if option A, all rental income, expenses, and profit are evenly split 50/50 based on original contribution amount.  

Would I use a simple JV sort of agreement between the 401K and myself to establish the roles and the split of proceeds?

In actuality, I have about $85K in my SD401K which in my area seems to be just shy of the deals I'm seeing. I end up doing them with my non-retirement money but I would love to be able to get that money working for me in RE without needing to go after assets that exactly match what I have in my SD401K.