Luckily there's still some decent fabricators about, and thankfully our vehicles have a proper separate chassis for such jobs.
Though i'm surprised no one has offered a replacement fully galvanized chassis for LC's, similar to those available for series Landrovers, maybe heavier gauge steel than OE.
There will come a time when the chassis on many 120's will be beyond a bit of fabricating and welding, someone could make a nice little business doing this.
120's in particular are worth spending on to keep them going, the sweet spot of medium duty Prados IMHO, good road manners driveability etc without too much electrical gubbins that will always empty your wallet at some point down the road when it goes wrong.
They don't seem to suffer the body rot issues that affected 100 series, and made before DPF's added another headache for future problems, plus pre March 06 (currently at least) not ridiculously expensive road tax, so in theory could be a comfortable 50 year life vehicle, a new chassis at 25 or so if needed plus maybe new body sills whilst the body is off if they've been neglected.
What we don't know of course is what the govt of the day, or the next ones have up their sleeve to force us out of our older vehicles and into some battery powered heap (i have no intention of ever buying and will walk instead), ie higher road tax rates (free VED as it ages still?), higher fuel duties, road penalties etc...the present and coming bans on being allowed into cities with older vehicles are music to my ears, if i never saw sight nor sound of another city for the rest of my life that would suit me fine.
Fortunately, our vehicles will always find buyers in other more sensible parts of the world if and when they are banned, unless exporting the wrong vehicles is made illegal in the future which wouldn't surprise me.