hi scotty , i have a 55 chevy belair . it has a 305 ci nova eng with 350 trans . it starts and drives fine but after about 20 mins of driving it develops a miss or shaking in the eng , worse with at idle. the eng is a napa rebuild with about 5000 miles on it. i'm not sure what to look for but thinking it is a valve out of adjustment. it has a hei ign thanks in advance norm