Project Nippon

Rob, if your budget is sub £1k, don't bother with an all jap build. It will not happen. Sorry.

In theory you could do it by converting a random jap road frame. You could also save some money here and there going second hand, using sugino messenger cranks, maybe...

rob, i wouldnt settle for second-rate parts over having every single thing njs.
if you want full njs and have a small budget then you might just have to settle with your build taking a very long time. if you could settle for small things not being njs and some things not even being japanese then you could easily build yourself a very nice bike for around six or seven hundred quid.