my method for altering a frames width is to measure the width.
say its 110mm
and it needs to be 135mm. a difference of 25mm.
then put the bottom bracket shell in a vice.
then get a scaffold pole. put it on the inside of the right drop out, and the other end on the right side of the seat tube. then lever away from the centre line. till the measurements 110 + 12.5= 122.5mm
then put the pole into the left side and open it to 135mm.
If you dont have the frame set to the width of the hub, it will stress the axle and bearings. Also it'll mean that the wheel will be a pain to remove. And you know it'll flat on a cold dark wet night.
Might be a good idea to move the axle through the cones a bit. as the Raleighs drop outs arent the thickest metal. move the axle to the drives side a couple of mm. be easier to fit the spacer you mentioned.
Ive got a Hercules shopper bike. Its got a loop tail rear frame. had an idea to fit a 9 speed disc hub to the rear. Ive widenened the rear end. Its a Raleigh brand frame, but has a normal BB thread. might have to mod the drive side frame more to get the chain on. An 11 to 32 cassette and 52 chain ring, would give 32" to 95" gears. might get by with a short cage mech too. So would have reasonable ground clearance.