Actually, VW are pretty straightforward and do not hide very complicated information (such as engine type).
The first digit "1" indicates a Type 1 vehicle; Bug or KG
The second digit indicates body style; in your case a "1" is a sedan
The third digit "9" indicates the year of production; 1969
The remaining digits are simply the sequential number of production; your Bug is the 66,831st produced in the 1969 production year.
Much more production information can be obtained by writing to the Stiftung Automuseum in Wolfsburg. That will also cost you some Euros.
As to the engine........look at the bottom of the generator pedestal. There you should see a single or double letter prefix followed by six or seven numbers. That is your engine serial number. It will tell a story about the engine AS IT LEFT THE FACTORY. Of course, with 38 years in between, any number of things could have been changed in that engine. More likely still is that your engine is NOT the original. Post up the engine number and we'll tell you what we can.