63 is easily achieved and will not harm the reliability - seems to be what the NSR was designed to produce before it got strangled.
The worst culprit seems to be the airbox, and opening that up gives the best power gains.
The de-restriction will obviously let the bike make top speed, though you can of couse just fit the speedo converter which is (1) far easier, and (2) looks better than putting a sticker on the KMH readout.
The standard pipes make good power, though the stock cans can be improved on. TYGA and the like are good, and weigh less, though it seems Honda made a damn good job of the original pipes. Don't forget that all aftermarket pipes require the bodywork to be spaced out or trimmed as the right hand chamber clashes with the right lower fairing.
The reeds (fitted to reed cages!) and stuffers seem to improve mid range response with no downsides.
All of this is bolt on stuff and will net you 62-63hp. If you want more (and I'd ride it first as you'll probably be happy!) then you need to start cleaning up transfer ports, optimising the castings and mucking about with dremels. If you cock it up though, you can wreck your crankcases.
Do the bolt on stuff, and see what you think. If you want more, then you'll need to pay a lot for a pro to do the work, or be very carefull and do it yourself. As you approach 70hp though, remember the reliability may start to suffer...
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