The custom made T.K.R.J. looks great, this bike is really cool!
The frame geometry is up to date, to the motor I have not seen
this engine here or heard anything about the RX model.
The threat questioner should tell us probably something about his manufactoring skills too, then it would be easier to post a good hint.
(I have a lot of respect about the improvisation skills the folks have in asia).
Starting trals with an modern enduro like bike is IMHO not a so good idea,
the frame geometry and engine power output is too different. If you have many skills and some machinery it is possible to create a trials machine of
an modern enduro engine:
But even the frame work needs a lot of machinery work to get a good result:
Then you have to make a lot of changes to the gearbox and the
power delivery too.
To rebuild an older engine is IMHO easier, also to build or modify a standard tube frame, like this Stornello engine of the beginning 70's
with a home made frame:
I would try to get one of the already mentioned Yamaha DT 125cc from the 70's to 80's models that may be even available in your home country
and take that model as a start. Any trial specifiec parts you can take from a TY 125 or 175cc model. These bikes or parts to this bike model are easy to get in the UK and not very expensive.
The 125cc TY:
Later on you can rebuild this bike with a 175 or 200cc cylinder/head/piston and do some small other changes too, (chopping of
parts that you don't use for trialriding, ...)
The result can be something like this:
Very competive even nowadays!