The coupe doors are the same length as a two door sedan I believe, but the similarity ends there as the roof height is different, so some custom surgery on the window frame will be required, which means that the glass won't fit any more.
Moving the pillar is also one of those jobs that is not for the faint of heart.

The side window shape of a two door is also completely different to the back door window opening in a four door body so more major surgery & more glass that doesn't fit.

To be honest, you could spend the price of a new Lexus on doing it & all you will have in the end is a cobbled up & cocked up four door hack up.

I believe that it would be much less expensive & much easier to actually import one from Japan, either as a car or a body shell. At least you will have a real one to begin with.

Young blokes very often have ideas that their tallents & wallets cant back up & when the going gets tough, what was once a perfectly good car gets scrapped.

I suggest that the car be rebuilt as a 4 door & once it's on the street, find another body shell & do the two door number on that, assuming you can get him out of this one.

Have a look at the car in this link & compare the 'C' pillar size & shape as well as the rear side window shape, noting the stainless trim & general layout.

Four door to two door, .... massive job.

Yes, the GX's also came in the 4 door versions in ZA. I take it this car is in ZA?. The car seems to be in the same state mine was in when I first got it. Strongs, and keep it up, soon you will be driving a rocking little car...

Is it a real GX? I wonder what the origional colour looked like in it's hey day. It reminds me of one of the 'rust eze' cars crom the movie 'cars'.