Going on a little further from dd's advice, I always found it much easier to turn the engine over by hand by removing the spark plugs. That erradicates all the resistance (compression).

You really need to have a good look before you declare the engine seized.

You'd need to give a bit more information to get a reasonable response.

yeah down at your local car delaer, but it comes with a rubbish car, not a datsun

hmmm ok ill give it a go thanks for your help !!! i have a feeeling im stuffed know anywere good to buy a twin cam ???

With transmission in nuetral, you should be able to turn the engine by hand either by:
* turning the fan, which is difficult
or
* by a wrench on the crankshaft bolt
If it won't turn, remove the starter and try again. If it still won't turn, disassemble the engine and find out why.

i have skimeed the head all is good in that department complete new head gasket kit installed. but wont turn over im thinking that the pistons have seized and i dno how to free them ? or if im totaly stuffed?

No need to fit over-sized pistons. If it is only a blown head gasket, prep the block face and head face well, and fit a new gasket.

Gday new to this site just bought my first dato and had head gaskeet crack and now sized pistions advice or help asap??????????????????????