Howdy Scottie:
All OEM exhaust manifolds for 144/170/200 & 250 are cast iron. There are very similar from '63 to '68ish. After that they have subtle difference due to EPA acommodations. '65 & '66 are good casting years to use as they have fewer bulges and taps for smog stuff, yet have good gusseting and are more crack resistant than earlier manifolds.
They will bolt up to a late model 200/250 head. Late model 200 & 250 heads are the same.
Adios, David