High guys was talking to the guy thats doing my ute,i want to put 4" on the front but he said that the engineer requires the front to be 3/4s the size as the back.Can anyone tell me whether or not is this true.

I don't know whats required but why don't you get some cheap 15x6 wheels to get it through rego and then put on whatever you like afterwards? You should be able to pick up some silvia wheels on nissansilvia.com for around $50 for a pair.

anyone know?

haha you're going to trust the internet over the certified engineer who's practically the one registering your car? but yeh, pretty sure that's true
drag setup im assuming?
like 1200ute said, just buy cheapies for rego