Also, at the balloon, if the Vendee is unable to produce, you can simply renegotiate another Land Installment Contract keeping the above two prongs in mind.

Usually the bank makes them produce his qualifications. 

There are several products to buy in the store or you can buy a small extractor from any big box store.

Using comparable sold properties with similar condition to your end product, within a 1/2 mile (sometimes a little further), less than 6 months old, within 20% of square footage, not crossing major boundaries ( high ways, school districts, city lines, etc).

Generally the conventional, non FHA loans have been cheaper and preferred and FHA was a backup for those that could not otherwise qualify for those loan products.  

So I was wondering if there are any particular things you can do to make the product irresistible to buyers.

If you really want this place, maybe you have enough to put down so that it produces income from day one.  

HELOCs are typically bank products, not mortgage company products, so they have a lot more leeway in how they underwrite them. i.e. they are not trying to meet some government organization's criteria, just their own.

How are you getting 5.125% fixed for 30 years on a commercial product?

Have a blessed and productive day!