The classes are broken down by body year,body modifications,engine size ,fuel and blown or unblown. I dont have a rule book in front of me so these details may be a little off but 1900-1948 run vintage class, 1948-1981 run classic and 1981 up run Modern class. Production can have no aero mods that are not factory thru with classes in between all the way up to streamliner. Engine sizes are broken down into ranges and given a letter designation. AA over 501 CID , A class 500 inch and under, B class 373-439 CID, C class 306-372 all the way to K class up to a whopping 30.99 cid. Next is fuel which is either sealed event racing gas or you run fuel class which is Nitro,ethnol, methanol,E-85 or N20, Diesel might even put you in fuel class unless you run specific diesel class. Then you have blown or unblown and that includes turbos So long story short the f-150 if it is factory stock except for safety mods and engine up grades and runs on event gas should run E/GBPP.
E-between 3-4.2 liters
G-gas
B- blown(turbos)
PP Production Pickup (unaltered factory aerodynamics)