gmc sierra plugs

[Deadcalm]

Hi im an English man just moved to the states brought a 86 gmc c1500 sierra classic with a 305 and a 700 r4 trans . with 116000 miles on the clock . i know absolutley nothing about these vehicles and i am trying to find out a few things i have a problem with the fuel gauges not registering right and want to replace the plugs and leads but cant find out what plug i need and also the gap that it should be . hopefully someone can help me .