The MEP-804A and MEP-804B may have either the Libby A1 or a TRC A1.
Depending on which is installed when the generator was built the correct R16, T1 and Voltage Adjust potentiometer are installed to match the A1.
Since you have a Libby A1 then you need to check the following to be sure your generator has the correct parts in it to work with a Libby A1.
For front panel AC Voltage Adjust control the back of it should look something like this.
Somewhere on the back of it it should say "10KΩ" like line 2 in the photo below
View attachment 827540
Next to check is the resistor that on the back of S12
It's suppose to be a 3,000 Ohm resistor
If it has colored bands on it then it will look similar to the picture below.
If it has colored bands they should be Orange then Black then Red then Gold in that order.
View attachment 827541
The third item to check is the T1 transformer.
It should look like this and ought to me marked with "122-7182" or "5950-01-370-3328"
View attachment 827542