You cant go wrong if you are carefull and make sure all the bearings sit on the pins/rings that locate them and the gears sit on the selectors.
IF you removed the selectors from the drum you have to be carefull to get them back on in the right order the right way round and make sure the clips holding the pins are in right, the manual shows this.
STEVE looks all there except possibly the pins and clips that locate the selecors to the drum, but they were still available last time I looked and will be in the box you already have anyway.
HINT It used to be cheaper to buy a 550 bottom gasket set and seperate 500 clutch cover gasket than a 500 set from Dave Silver, 06111-374-000 i think (top set 06110-323(374)-000) I may have the 06 numbers the wrong way round but the price will soon tell you!