The A-65 Overhaul/Buy question

Here and elsewhere I've been exploring the possibility of buying an
a/c with an A-65 engine which has exceed TBO. We've learned the TBO
figure isn't gospel, but it probably isn't a bad idea to be
thinking about an overhaul. For the purpose of this discussion, let's
assume something has occurred and it's time to open the case. Since
the engine is old, and you've invested in opening the case, you have
to think overhaul.

A look thru the trades show mid-time engines can be purchased for
around $4,000 and recently O/H engines for $7,000.

It is possible after the engine is opened and inspected one will be
faced with repair costs that exceed the cost of purchasing a recently
O/H engine.

My questions a
- How much do I have to invest to be able to make the overhaul or buy
decision? (My experience is (in the DC area) opening a case,
inspecting, closing it up will cost $3,000).
- How can I cut the investment?
- What decisions have to be "outsourced" to an engine shop, i.e.
the decision is outside the ability or willingness of a small shop to
make the decision and provide an estimate?

- Mike