http://www.tyga-performance.com/pages/mc28wiresplice.php

your speedo will turn into a temp gauge which will mean the fitting of a digital bicycle speedo (or if you are fontyyy nothing), and you will loose the oil light and neutral light.

the pipes are restrictive on the 28 but i beleive to get anywhere near the 57 figure you will need to deristrict and modify the airbox, most of the modded NSRs (pipes, airbox,wire splice) hit around 63BHP it is unusual to see above this with out going to the extremes that you mentioned porting ETC.
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MC21SP - Roth-tax
CBR400 - track
MC21R - sold
MC21SP - sold