Hello, I’m a new member and this is my first posting to this forum. Recently, i acquired a 1965 Mustang with a 200 six. This car is some what odd, at least to me, in that it has a cylinder head unlike any I have seen. It has adjustable rocker arms with hydraulic lifters, which I understand is not uncommon, but it also has threaded brass plugs in the factory bungs next to each exhaust valve on the exhaust side of the head. Does anyone know what purpose these serve? The casting on the intake log reads C6DE 6090 B X5. Thanks in advance!