Petrol specs

I'm proud to announce that I've gotten to the point that i need to worry
about what sort of fuel I put in my car.  Until the next time I
inabilitate it atleast. So since my car is a '61, and was designed for 97
octane leaded gas, what do you guys use as a substitute?  I'm really not
in the mood to buy an $800 aluminum unleaded cylinder head.  Considering
my whole car cost me $700...

-Ryan
'61 Midget GAN1L/4506