Re: replacing 351 with an I-6 300
Here are the tricks to the swap. You will need a radiator out of a truck with a straight six. The inlet and outlet are on opposite sides of the V-8 radiators. New motor mounts for the straight six. No other bracketry will be needed for the motor mounts. You will see when you get them. Make sure you get all of the accessory brackets for the 300, the brackets on the V-8 won't work. The alternator and P.S. pump should fit though. Get hoses for the 300 and with the correct radiator, they will fit perfect. For external parts, you can say the correct year of your truck (1985) and say it is a 300 straight six and you will get the correct parts most of the time. Some internal parts will be date specific. A few wires may need to be shortened or lengthened, but I wouldn't worry about that now. Good luck, Eric.
If it ain't broke, I can probably still fix it.