Hi fella, do you mean swapping the head from a plastic top to work on your ally top motor or do you want to get your car running with a whole plastic top conversion?
The former is easy enough mate, you need to-
Remove all the plastic top intake gear, throttle body, manifold injector rail etc
You will need to fit the exhaust camwheel and cam sensor from your ally top engines head onto the plastic topped head.
The thermostat housing needs swapping over as the sensor plug is different.
There will be a plug in the head where you need to fit your coolant temp sensor from your old head, this just unscrews from the head.
You will need to use your cam cover and rubber gasket from your old head too.
Also, check if your ally head has a small pipe welded to no4 exhaust manifold pipe, if so you need to use your old manifold gasket and remove a plug from the back of the head for the egr valve.
Think thats about it mate, if you need any help give me a shout
Good luck and take your time fella.