We always care about gross income, expenses, deposits, roofs, mechanicals, structural issues, survey, title, and all of the other things we should be investigating. 

In my initial offer, I requested to allow me to survey current tenants but seller denied under pretext not to disturb tenants.

(90%+, numbers change depending on the survey).I’ll believe the vast majority of scientists, and ignore the small percent who disagree for whatever reason.

I order to proceed I would have to do land markouts, surveys, and rezoning which can come to around $10,000.Does anyone have any ideas on what is the best way to capitalize on a property like this?

Check out the CBRE Cap Rate Survey (First Half 2016).  

Paying 81k for duplex. 11k closing costs (including re taxes, lawyers, title and survey) and figure I’ll be putting in about 20k in rehab...ARV about 140k. 

They would not grant a partial release.We had to time it so that they refinanced before they could sell the lot, but it worked out great for them.If you can wrap all the costs into the refinance (pay off the existing loan, survey, and title work) then it looks like you could pull off a "free" lot....or at least have a minimal investment in it.

Situation: Imagine a property in Fishers, IN (recently awarded safest place to live in US), a suburb of Indianapolis, IN that is surveyed as 3 lots and has two properties on the lot.

This seems to be a good starting pointWorld Bank - Bank Regulation and Supervision Survey

I personally love rentometer for surveying market rental rates, I find it to be pretty accurate.