i'd get the gas tank drained as it probably has water and other contaminants in it...fill it up with clean fuel then run the car for a short time then replace the fuel filter (to get any residue out)

i wouldn't switch to synthetic on such an older engine...10w30 will work fine but you may want to to with 10w40 to prevent the slow burn of oil (happens on such old high mileage engines as the piston rings wear out over time & use)