Howdy All:
Q- "doesnt it have the same intake manifold as the 250? it comes off?"
A- Yes, It is the same head used on the 200 and the 250. No, the intake manifold does not come off. It is cast on as part of the head casting. Your '68 200 engine is rated at 9.2:1 compression ratio. The '80 engine is rated at 8:1. The improvements in the later head and the DuraSpark II igniton will not be able to make up the difference from the reduced compression ratio. There is a sticky at the top of this forum about swapping late for early heads. There are two factors that you must deal with to get the most out of this swap- chamber volume and replacement head gasket thickness.
What is the casting code on the '80 head? You should probably get and use the carb on the 80 head too. It is a more complex Holley #1946 carb, but will flow more cfm @185, then your 1968 Autolite 1100, which were downsized to 150 cfm. The linkage on the '80 is a cable type that you may be able to use- from the pedal to the carb. this is where the later valve covers are useful- in providing an anchor for the throttle cable.
Keep the info coming.
Adios, David