knock the old ones out with a hammer
try and knock the new ones into place with a soft faced mallet so that you won't damage anything if you miss
then use some steel wheelnuts, fitted the wrong way round so that the flat face is against the hubs side and pull them through

you don't really need a spacer because all you do is put the disc back on again and use that, it's much easier just keep going until you feel them lock up into place
after a few miles recheck them as you really don't want them to come loose