The odds of that an engineer will say its perfectly up to code and it requires no changes is probably pretty low. 

The equities side is actually a hedge; you're really 67%-80% betting on debt. 

Your best bet is to borrower the downpayment (although, if your property doesn't debt service, you won't cash flow)

Probably 50/50 odds you might get money back going that route.- Tom

Rentometer as @Tommy Katzenellenbogen said would be another fantastic bet. 

It's odd to me.

I’m betting someone who rents out 1950’s homes in the Midwest would use a percent higher than 0%. 

It would never appreciate to where it would be worthwhile and great cash flows on paper but not gonna happenI would bet this is common in many of these other urban low priced areas.

If you're going down to the studs in the bathroom already, tearing out the window trim/stool/apron is probably the best bet.  

Sorry to not offer a connection, but for this one I think your best bet is to find the "land specialist" realtor in the area and get a CMA.If you want an extremely precise number hiring an appraiser is most likely the move.