My question is what is the difference in the big block heads of 68 and 69 compared to 67. I know the 67 heads are a non quench type. Would it be beneficial to replace the 67 head with a later 906 head?
Incorrect , the 67 heads are closed chamber , making it a quench type , but your piston is probably too low in the hole to benefit from it unless you got lucky and someone was smart enough to use the TRW forged replacement and a steel shim gasket , then you got quench baby.
Beneficial to switch to a 906 which is an open chamber head and LOWER your already lowish compression ratio, NO not really.