I cant necessarily walk you through it, but
GET a 86/87 200x manual - not clymers get a Honda one.
You’ll need:
Valves/seals - head work
Top end gasket kit - oem is best but there’s others that’ll do. Full kit w/oring
Timing chain and guides (new guides are pricey) hope yours are ok.
The decomp arm seal is discontinued if I remember right, aftermarket is available though if searched for.
Your cam/rockers use them unless excessively worn (again pricey for new) if found.
Wiseco 10.25:1 piston- talk to shop to find the size to buy (DONT buy piston first)
Take the manual you get with you to the thrown (can) you know... and read
The trx200sx top end is basically the same except for decomp parts and something else too but the castings are the same.
Think that’s it now u gotta do some of your own homework.
First thing/ find a reputable shop to bore your cylinder.
I’m outa here,
Oh and NOTHING from 83-85 200x fits this top end, well valve seals do I guess
Take your time scraping gaskets off....and do not use any rtv on assembly
Shep