Initial timing

^^^^What he said^^^^

List out what this car has and what you are trying to accomplish.
There were some some small changes to the 225 in terms of cam and compression, which will slightly effect timing.
But if the engine was rebuilt, then those small changes are probably out the window anyway.

The big changes in initial timing relate to the emissions.
If you are using the original 1966 distributor then the timing curve is non-emissions (except California) and everything is simpler.

If the carb is a non-emissions carb, that's even better.

Bottom line is the distributor is the most important thing to know. if it was intended for initial at TDC and you set it at 10 BTC, it will have too much timing at 2000 rpm. And it was intended for 12 BTDC for a Feather duster engines and you set it at 5 BTC, it will be igniting little late and wasting energy at driving rpms.
So if you don't know this, then set it for a good start using the '66 specs, and then measure and plot the timing curve using a dialback light (or timing tape) and tach .