i know this is a 1975 engine. But is it a unleaded unit.
It now resides in Australia ,and our laws require it to confirm to the year that the vehicle was built not the engine . Can anyone tell me when your country 1st bought in unleaded emision regulations ?
PS its awsume power on leaded and even awsumer on unleaded . Small dogs sitting on console find them selves on rear fire wall unable to move

whotoo,

I don't know when all of the cars in the US changed to unleaded gas, but the first year for the Corvette was 1975. This was the first year that emission controls were put on the engine.

For unleaded gas, it's not the engine block but the heads that matter. For unleaded gas they had to have the valve seats hardened since they would no longer have the lead to act as valve lubricant and octane enhancer. The '75 used the same block casting and numbers as previous years...the same head casting as well, it's the hardened seats that make the difference.

If your block number matches the car's VIN, you're OK.