86 and 87 were the change over years from carb. to CFI (centeral fuel injection).
if a carb then you need to find the bugger, (normally on the fire wall or in the carb, sometimes under the truck) buit it will be straight forward two clamps and replace.
if it is the CFI 2.5, 2.8, or 4.3 then the filter is in the gas tank. (still follow the whole fuel line to be sure they did some weird stuff during the change over years. I saw one once that had CFI and a fuel filter mounted to the firewall on the passengers side next to the heat fan)
And then you start by getting most of the gas out of the tank, (run/drive it out or use the old hose technique)
then depressurise the fuel line, (this part is messy) by either pulling the line from the CFI or if you know where it is push the pressure valve relese (looks like a valve stem sticking out of your steel fuel line.)
DISCONNECT THE BATTERY
disconnect wires leading into the top of the tank.
drop the fuel tank (this is why you run almost out of gas)
I used a floor jack with a piece of plywood for balance.
once you get the tank on the floor you will have to pull the sending unit out of the top of the tank and the filter will be attached to the sending unit along with the fuel pump, main fuel line and the vent line.
replace the fuel filter and most people recomend that while you are in there replace the fuel pump and sending unit.
I also recomend that you replace those as most sending units will fail shortly after being exposed to the outside air.(I do not know why but they do).
hope this helps.
M.

locate if the filter is either in line under the hood and or follow the lines and see if it is behind a wheel well and it should use a clamp most likly a flathead screwdriver unless its been changed with a different clamp style