I'm no EFM expert, but I think that means the boiler is a 1959 vintage. They didn't come out with the Dual Fuel (DF) until 1980.
It's possible your stoker is from an earlier unit. I don't know the specifics but the early S-20 and S-15 stokers were different. Maybe that is why you had to make pieces? The blower housing should have a data plate on it. Get the serial number off the plate and look it up in this thread. then you will know what year the stoker was made.Dating S-15, S-20, S-22, S-30, S-35, S-45 stokers
Sounds like 4 teeth is not enough to heat your load. If heat calls take a long time and or the boiler temp is going down during long heat calls, the feed rate is to low. I would suggest bumping it up to 5 teeth, 4 air, then adjusting the air for a 2" ash ring during a long heat call.