[bigsixman]

GM aluminum heads were not very good back then comparing to today's technology. William is correct in his post about common problems and I will add some more.

The valve seats were not very good and many times fell out. The rocker stands were not very strong and often times broke. The heat treat process that GM used had problems and has been corrected in modern castings.

These problems often surfaced when the cam, valve springs or rpm limits were changed out for racing purposes.

They were the best at the time, but today they should only used by people required by sanctioning rules or correctness in a restoration or a period correct street car.