Lots of good advice in this thread OP. Something to remember and several of the guys have touched on this from varying perspectives;
- Receipts only show what was bought.
- Receipts might show how well it was assembled, predicated on who built it,
- How well the engine and car were maintained is more difficult to establish,
- Current condition of the car is essentially a visual and driving check point,
- How the engine was treated can be estimated with some diagnostic tools
- Diagnostic tools only provide estimations,
- Disassembly and inspection provide answers
Something else to keep in mind is that the majority of Cobra owners farm out their engine building. The use shops like Blykins and Kraft and sometimes backyard amateurs because engine building is not one of their strengths, only a hobby. This stuff is not like doing the Briggs & Stratton on your Dad's lawn mower when you were 10. The charlatans out there will provide you with a special type of headache — and spend a lot of your money for it.
Tony's (and most everyone else's) advise is excellent and you will be farther ahead, spend less money and get much closer to your desired outcome if you embrace it.
Ed