Mostly stock 340 engine what Spark plugs

I used to use Champion N9Y's but can only get them in resistor form. Switched to accel 114's some time ago and they seem to work okay. The 340 runs about 10.5:1 and the plugs have the correct coloration. Before the popular availability of unleaded premium gas plugs only lasted about 1500 miles before the engine started missing at high rpm runs.