Is it necessary to put a sealer on the gaskets when reassembling the heads on the engine or are the gaskets themselves sufficient for sealing

I take it you are using new gaskets,If not you should,
So the answer to your question is no,gaskets are used clean.

yeah sorry I should have stated they are new ones!
thanks for that

Just fit them then.

As above, fit them as they come.

Make sure the mating sufaces are clean and torque the bolts to the correct torque and sequence from the service manual.

all sorted lads thanks , should have it up and running shortly.