The bolts with the 5/8 heads are junk and will most likely cause you problems later. Using the original bolts is better than using the junk bolts. Every time you do a trial assembly the differential bearings should be shimmed tight enough that it is hard to pull the differential out by hand. On the final assembly the shims should be tight enough that you can not pull it out by hand. As long as your backlash has been within specs and the shims have been tight on each trial assembly everything should be good.