Not super difficult, but you do need to disassemble the distributor somewhat... pop off the cap and rotor, there is a small roll pin that will let the first set of plates that you see be removed from the housing... Underneath that is a plate with two screws and two slots. You must loosen the two screws, rotate the plate to close up the slots a little and then retighten and reassemble.. you can buy timing keys which are plastic do hickeys you put in the slot so that you know exactly how much to close it but I've never found them to be very accurate, somewhere somebody had a chart with certain size drill bits you could use to set the space... Otherwise you'll just have to close them up a little put it back together and see what you get, and if you need more you'll have to repeat the process...
This is an old distributor I have just to give you an idea, rotor is off...
Pulling the top guts out... there is a small roll pin underneath that holds this on the shaft and two screws on the outside of the housing
Pencil is pointing at one of the slots, at this point they are all the way open
Here they are completely closed. You can see the two screws that need to be loosened, your slots should be open just a little bit if you don't have the little spacer gauge you will have to experiment with how much to have them open
These are Firecore's instructions...
As a side note, this is best done with the distributor out of the engine... Be careful not to pry hard on anything when you're taking it apart and you shouldn't have any trouble hope this helps good luck!
