To be honest looking at the different spec's [Travel / Springrates] between the two models, you would have to be Travis PastramiOnRye to notice offroad ..
{your not Travis, are you ?}
Not sure about rear wheel, a standard DT RE 04 on rear wheel should fit ? I THINK they are the same Hub dimensions & disc position etc ?? Borrow a m8's rear wheel & see if it fits !?
Front .. Problem ... as i THINK different Hub dimensions ... the disc & caliper are certainly bigger / mounted wider out towards the rim on an X for the big SM brake ..
One of the guys here has a 21 inch trail rim, spoked up to a standard X Hub & it works well ... [bit overbraked for trailriding, but you get used to it] !!!
Check a back ... see if it fits
Get a 2nd front Hub & Disc, spoke up to 21" ..
Best of both ..
But you 'WILL' come off & scratch your shiny X to feck off road riding !..
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Blue - DT 125 RE - '04 - First Of The Leccy Start Lanza'Like Bikes !
DT-R or RE forks + both wheels and also the front brake set up.
Make sure you have one of those stands that goes under the bike which you put your foot and then if you have the above parts you can simply drop the complete front end out (fork legs + wheel + brake) and put in the DT-R set along with the back wheel and disk for some off-road action.
Lucky for you DT-R parts are cheap and you could get a tidy set up for maybe less than £100.