I have a Barina engine in mine I scored it for nothin' just had to pull it out of a mates car.
They require a little mucking around to change over parts as the barina is an east west mounting the dizzy is straight out so that needs to be changed to a Suzy one, as does the cam! because the keyway is wrong for the Sierra dizzy, the oil pick up as said is wrong as is the sump, inlet manifold is a throw away just replace with Sierra one and carb to. You will have to swap sierra water pump nose (the tube at the rear of the water pump) to sierra one but if you leave the actual water pump and pulleys this makes it an easy job for fitting an EL 110amp Alternator later otherwise replace W/Pump as well all parts are interchange-able not a hard job at all! You might as well do all the gaskets etc.. while doing all this saves worrying 'bout them later! Cheers Robb.

Oh yeah! fuel pump is useless as the barina's are elec pump so will need to run one of these and if running barina pulleys the sierra fan won't bolt up so will need to make a new spacer or run a thermo!

You need to give more information about your vitara is it a swb or lwb? 1.6 carby or efi?

Why would you want to put a smaller motor in?

It would be legal as long as it is mod plated / engineered
Cost would depend on the price of the motor, mod plates / engineering, how much work you can do yourself.

ive got the carby motor, ive been told the injected 1.6 out of swifts are twice as powerful and better on fuel

unless there is some kind of great reason for you keeping your car your better off selling it and getting an injected vitara, heap less pain

x1000000 why didnt i think of that earlier?