it will physically fit, provided the heads are actually 66 units and not the earlier ones with the different bolt size and angle.
however, the port match is going to be horrendous.
and if you've got a stock cam, and you're running what i'll assume is a big carb for that manifold it's going to run not great at all.
Edit: what carb?
maybe it's useful to you and you can keep that and sell the manifold and get something more appropriate.