Howdy All:
In general it is throwing money away to use a higher octane gas then needed to control combustion. There is no more power in higher octane gas, just additives to allow it to burn slower. Your fairly stock '65 should run fine on 87 octane gas. If it has an Automatic trans you might want an edge.
You can minimize the risk of the ocassional ping or Knock by-
*running a can of fuel system cleaner through your tank periodically. Some will tell you to use water to remove carbon build up in the combustion chamber, but that doesn't do anything for varnish and calcite build up else where in the system.
*run spark plugs that are one step colder than stock specifies, especially in hot summer and sustained hiway driving.
*make sure you cooling system is up to pare and working properly, especially in high stress/high heat situations.
*make sure you ignition system is in tip-top shape and that your initial timing is set where you want it.
*a cold air intake system will help with knock resistance as well as more power.
If pinging is audible often, try reducing your initial advance setting. The trade off is that this will reduce power and mileage. With your stock "Load-a-Matic" distributor I would not be surprised If you were to tell me that you almost always hear a rattle in transititions from cruise to acceleration. That seem to be the nature of the system. If it a Calif. Emissions car it is farther hampered if thos systems have deteriorated over the years.
IIRC the true compression of a '65 200 is about 8.7:1 as opposed to FoMoCo advertizing of 9.2:1. So comparing today's 87 octane gas to standard leaded regular of 1965 of 95 octane, the 87 octane gas should be fine for your engine.
I hope that is helpful.
Adios, David
