They wont! Unlike the R34's with the interior MFD, it'd be really difficult to spot a nice conversion complete with guards, wheels, spoiler, bonnet etc. Only giveaway would be a quick peak under the bonnet. It'd look good, for sure and I've seen a couple of nicely done R34's over here. Not seen a R33 yet though.
However, who would want to go to all that trouble and then drive around like a Grandma? Not to mention, if you did race and got beat you'd have a lot of people going around saying how (for example) their S15 just whipped a GTR's ass...