117 model is 74 Mk7 125 pursang. Same frame as 120 model 250 Mk7.
Looks like 74 swingarm to me. It was 75 Mk8s that had the bottom shock moved forward
If its a 117 bottom end, the 250 top end goes straight on. Std 117 (125) top end had the old style round 9-fin barrell. Looks like 6-fin 250 barrel on it to me
117 bottom end had closer ratio gears (1st - 3rd), diff primary reduction (geared down more) & smaller dia crank which is balanced differently to 250, so may well vibrate a bit w 250 top-end. It would be worth checking.
Forklegs look like Alpina in std pursang/alpina clamps. That setup is fine for an Alpina but would have too much offset for my liking for a pursang. It reduces the self-centring effect which may well cause headshake in the rough. It also moves the front wheel noticeably forward, changing the weight distribution & wheelbase & would probably cause front end washout (you don't have as much weight over the front wheel). But its easily fixed if you can find some pursang/frontera sliders.
I agree w others above. A well set up Mk7 250 is a beautiful bike to ride. As good as anything in the class. Being very light & 'flickable' & w beautiful powerband, they explode out of corners like a scalded cat. They're very easy to ride & don't tire you like other heavier bikes.