i have zero idea why your posting this on a ford site, as opposed to somethign like,
www.nissansilvia.com where this information is readily available, and alot of people on that site have completed the exact conversion your talking about.
so yes it can be done, depending on what you want to acheive would be as to why you woudl want to do it, the 6 can easily provide 300 rwkw whereas the sr20 with the same 300 rwkw wouldnt be driveable by any means on the street.
still... why ask on a ford site a blatent question about nissans ?