only ever ran one tank of 10% ethanol thru my GT - ran phunky on the blend. Throttle response was not as crisp, and the engine note 'changed'.
Kristi - there is no way to tell if you have seats sans a teardown. Best bet is to run it 'as-is', and deal with the problem if and when it arises.
It always helps to have the records of work done on the car. If a restorer is even half-serious, he keeps all of his/her receipts of work - makes appraisals/insurance settlements that much easier (assuming the worst). A documented resto adds value to the car, so keeping the records is important.
Maggie the Opel has all her records from Day One. the original owner paid $2600 for her, and traded in a '62 Chevy for $90. Her A/C went in ten days later at the local Firestone store - another $280. It's stuff like that which helps document the car.
The PO of Emmy probably handed over a big stack of receipts. If hardened seats were installed, they should be on one of the reciepts. Dunno when it was done, but most shops charged (this is a few years back, mind you) about $20/hole (there are eight) for seats. An obsessive owner would get all eight done - the average Joe would get four done (only the exhaust valves).
In a typical head rework, the valve guides are another $20/guide, valves go for about $10/ea, and a three-angle valve job is another $100. So... The whole bill for head work *should* be in the $300 range - more if there were problems.
Also hidden in that stack of bills *might* be a record showing about $300 (or more) for a set of pistons. If so, the PO might have upgraded to hi-comp flat-top pistons - this would explain the pinging.
Going thru the bill stack is neat. It's a history of what went in the car - can tell you a LOT about 'what's in there'. Betcha Stanley P's bill stack is over 3" by now!