I've come across some info that suggests that '63-64 273 intakes and heads are different than '65-68. Is there any? More performance,less-interchangeability?
No 273s in 63. 64-69 were the only years. 273s went from solid cams to hyd cams in 68. 66-67 920 head is the best head for a 273. 68-69 the 273 heads were open chamber.