use long axle as the short one and cut down the long one by 155mm, or by 145mm and have 10mm of the spline cut off the short axle, this will get teh pinion pretty much centred compared to just cutting the 155mm off the long axle

this should get it to the right size for a 1200

the only problem with these axles is you cant cut the short one down, as you need to cut down at least 110mm to get past the under sized part of the axle

demo, you might be able to get some r31 axles cut down to the size you need, but its unlikely that the housing will be the right size in the right places, as you need to use the short r31 axle without cutting it down