Could you set the plug gap higher than 35 in a 1978 Chevy 350?

No, you should not set the plug gap higher than 35 thousandths of an inch (0.035") in a 1978 Chevy 350, or likely any other small-block Chevy of that era. Going significantly higher risks misfires, poor performance, and potential damage to your ignition system. The recommended gap is usually between 0.035" and 0.045", but exceeding the upper limit can cause problems. The manufacturer's specifications or a reputable repair manual for your specific engine will give the best guidance. Using too large a gap makes it harder for the spark to jump, leading to incomplete combustion.