I can't take it out without a penalty, but I'm not sure where to put it or if I can roll it over into an account where I can make money on it until I retire or find my next investment. 

This form may be served prior to or concurrently with a 15-day notice seeking payments due between March 1, 2020, and Aug. 31, 2020, served on or before Sept. 30, 2020.More info here: https://caanet.org/ctra-informational-notice-must-be-served-by-wednesday-sept-30Perhaps another reason there isn't more discussion on it is because people became more focused on the federal CDC eviction moratorium, which came out almost immediately afterward. 

That could be one way to access the funds without tax or penalty and just do a cash deal.

TLDR: Seeking advice on whether/how feasible purchasing a three-unit RT-4 to convert into owner duplex and one income unit is and still qualify for historic tax credit adaptive reuse incentives at federal and state levels, and welcoming any service provider recs to make it happen.The property under consideration: an 1880s 3-flat with a full unfinished basement. 

Yes you can withdraw from retirement accounts, penalty free.

Please be sure to select a Solo 401k plan provider which allows you to take a loan and will prepare the required 401k loan documents.The repayment terms are equal monthly/quarterly payments (as you prefer) of principal and interest (e.g. prime + 1%) spread over a 5 year term (or longer if you will use the loan to purchase your primary residence).There are no prepayment penalties and no restrictions on what you can do with the proceeds of the 401k loan.Please note that you are obligated to pay back their 401k (regardless of the performance of your real estate investment).As an alternative to taking the loan, you could even purchase the investment property directly using funds in your Solo 401k (assuming you select a Solo 401k plan provider which allows you to invest in real estate).

I'm also concerned with my very unique credit, that they too will require more collateral/higher interest rates from me to issue the loan, which will most likely leave the CoC less than 2%  I think it's best I seek a partner for this deal, someone who is eligible for a Traditional loan.

My investment is a house-hack, so I'm here now, hence the 5% loan and will seek to do another next year and so forth.

Goal is to seek out safe neighborhoods within a 25 min drive. 

Some things you are saying contradict tax code and leaves you at audit / penalty risk.