The Silvia is using SR20DET, and I agree with your analysis. And
I won't be surprised if it exists, in which case I'm not very
interested, because it has been done long ago in other countries
e.g. Australia. In fact the US has a model with a FWD configuration
(it's called Sentra there, not Sunny), you can easily buy that
engine off eBay.
http://page.auctions.shopping.yahoo.com/auction/85638443?aucview=0x23