i lift the bike up high, get wheel under the gard, if its a belt it's harder, chain is easier. with belt remove the belt gards. put wheel in place. i have a thick block of wood to lift wheel up sit it on.
then make sure brake pads are open & eather side, loop belt or chain over drive sproket get the disc into caliper get spacer in place have wheel up on block then while holding spacer on brake side in place, lower the bike till axl hole lines up put a bar or an old axle in one side to hold everything in line then push the axle through on other side. i always coat with anti sieze.
thought i'd mention , mine is easy as i have an out rigger bearing support on drive side, this bolts to outside of drive sproket takes the place of the stock loose spacer, & it has a sealed ball bearing press fitted inside. best thing ive done to upgrade a HD, been doing this since early eighty's never bent an axle or had a bearing fail yet.
think about it, you got a wide spacer then the swingarm , when the drive belt pulls on sproket it can put a lot of stress on axle. with this set up you have a machined block of alloy the sproket bolt patern drilled in it's machined off then sealled ball bearing press fitted in its bolted to outside of sproket so in effect you move your wheel bearing up beside the swingarm on drive side, you get extra support & a extra bearing supporting all the weight. & as a bonus makes solo wheel change easier.
I agree Hilly, but guess it would add costs. First time I did that was with a striker shovel it bent axles all the time. Tried to get stronger axles made up but they bent too , then a bike drag racer from QLD built a new drag bike with a huge slick. I looked at his rear axle and it was not that thick. Asked if he bent axles & he said no. Told him about my prob & he said get the wheel bearings as close to frame as possible. I thought about it, told a m8 & he said give him rear wheel axle & swing arm .so took them off & he made that. No more bent axles. But new HD have a thicker axle but that out rigger bearing would help in more ways than one