8-9-10spd cassettes are the same in terms of overall width, some Shimano 10spd road cassettes require a spacer. You won't need any spacers to run an 8spd cassette if the freehub is listed as 10spd.
But as babylou said the rear of that frame is most likely 126mm. If the new wheels are 130mm you can spread out the rear and you will be fine (if you want to do some research there are millions of forum threads about this all over the internet).
However if the new wheel is 135mm and your frame is 126mm personally I would not push it that far even though it's steel.