All good advice above. Before you get to far along however, give some serious consideration to pulling the front cover and replacing the timing set. If it still has the stock phenolic cam gear and it's worn enough that the fibers have plugged the pick up screen then it's done. There a couple of ways to verify a worn cam gear. Remove the fuel pump, turn the crank counter clockwise and reach in through the pump arm hole and check for chain tension. Another way is to use your timing light and check for smooth mechanical advance from about 10 to 12 degrees initial up to about 30 degrees total advance. If the timing advance is irratic the cam gear is worn or the mech. advance is worn or dirty. The bottom line is that in an engine that old the factory cam gear is almost certainly worn out. Steel replacement timing sets are quite reasonable and cheap insurance. Don't forget a new front crank seal.