Because the property is 2 units, acreage, outside of somewhere like "Selma", rural, manufactured, unknown foundation type (auger, concrete, cinder block, engineered...?) 

There is a lot of unknown things but I would love to leverage experienced investors who have done this successfully.

But now the status has changed to unknown and the sell date on it is December 1st 2016.

All the unknowns were scary when starting and new unknowns still are, but we keep pushing through fear when it sneaks up and always are happy we did.

This is what robo-callers use to leave you pre-recorded scam messages about back taxes owed or unclaimed money left by an unknown relative.

I want to dive in and take it on but am a bit apprehensive because of the unknown and lack of experience which I'm sure most newbies are. 

Again, I'm a newbie to the field, and if this is too simple for someone with your experience, I apologize in advance :) I understand the fact that Real estate and notes are a bit complex (exactly what I'm starting to feel as well) and difficult to understand the unknown pitfalls and for a new investor it is easy to fall into the rabbit hole.

. $100/sf on the construction side is fairly accurate, but there are a lot of unknowns that need to be figured out before you ever start construction that will significantly impact cost.

The unknown is, will they survive?

For the loan of you 100k you are getting 96k equity, 70k returned after an unknown period of time, and getting 21% on the little bit of money you still have in the deal.