Kz 400 neck and forks

Hi guys need to the site been reading a lot on there I wonder if somebody can help me. Study new project with a KZ 400 im trying to give it a wider look in the rear what's the biggest tire I can put on their stock. And I want to give it a wide glide look in the front I useing a more modern bike as donor that would fit that KZ neck

I appreciate any help or suggestions that come along my way

pretty much any front end you want can be converted to fit your bike .the length of the front end and wheel combo in comparison to the stock front end is the biggest consideration.
i can't help on the rear tire ? tho.

leon