Engine swap??
 

Will a series 4/5 13b turbo engine, fit in a series 1??
if soo what other modifications will i have to do??

Yes. Check the 1st gen FAQ for info.

Off hand, you'll need a GSL-SE front cover, GSL-SE oil pan and pickup. Then you'll either need to match the flywheel and clutch stuff to the transmission you have, or swap in a TII transmission by changing the tailstock and shortening the shift rods.

You don't need a GSL-SE front cover particularly. Any pre-FC single-distributor front cover will work if you have trouble sourcing a GSL-SE one. The only difference is that the GSL-SE front cover has a 4-line OMP and the others have a 2-line one, so if you go with a 12A or old-school 13B front cover, you'll only use the oil injectors in the intake manifold and block off the ones in the rotor housings. I believe the 12AT front cover also has the 4-line OMP. You'll then need to fabricate an OMP lifter rod, or just wire the arm to the 9 o'clock position. Or you could just premix and not worry about any of this.

You also need to account for the extra length of the 13B. Easiest way to do this is to get one of Racing Beat's front mount bars. Maybe someone in Australia makes them too, I don't know.