Still, I must agree with the others. You will have issues with the steering box and possibly chassis width - drop it into a HR or similar where you can get conversion kits to suit.
Either that or sell it - you'll lose money but say you only got $5-6k that's heaps when you're talking jap motors... and you'll piss in 300hp with pretty much any one of them.
Or, better again... accept you were not only wrong on the V8 vs Jap motor thing, but accept that you were wrong on the car vs bike thing. Get a bike. Ride a 250 (which is probably faster than a 308-powered anything) for 6-12 months then if fast is your thing you can pick up any number of 10/11 second bikes $4k in completely stock trim and get insurance for a couple of hundred bucks a year.
My GPZ900 was cheep (like the budgie), ran 117mph and was $200/year to insure. If I ever buy a car again it'll be a ute or a van to ferry bikes to the track!