Got the cases reassembled on my CT3 today after a few weeks working and waiting for parts. I was feeling accomplished and ready to keep going... until I saw that I forgot the shim on the RH crank and it stopped me dead in my tracks.  

 

What are your worst "I'm an idiot" moments to make me feel better?

Oh damn, feel for ya but i'm sure we've all been there in one way or other. I'll have a think but probably won't need to think hard to be at the top of the list.
If it makes you feel better the right side case will come away easily as the bearing is a sliding fit & is held tight by the gear & nut. Be careful to keep everything over in the left case as you the coax the right side off if you want to go that way.
Just a thought though & crank being tight in the left, you might need to tap the shaft once washer is in place. Take the screws up under slight tension then tap the shaft [without damaging threads]. Then tighten screws or give another tap if not over far enough. Hmm--'think' that's what i'd do.
Or a crank puller to pull it further over into the left first. Whatever works for you.

I’ve done the same thing before 

It happens. There's a motorhome forum  I'm in. A guy just changed the oil in his motorhome, with a Ford V10. He poured the new oil in, but forgot to put the oil drain plug back in. He started up the engine, and let it run until it stopped. His engine is now a boat anchor. In fact 4 decades ago I was changing the oil in a Toyota pickup, and as I was pouring new oil in, I  began to see oil gathering in the gutter. Thankfully, the only damage was an oil stain to the street. I remember that mistake every time I've done an oil change since.

I didn't spitpin the kingpin castle nut on my 55 vauxhall--& the front fell off haha--well, it lay down on the road sulking in the middle of the night, 100 miles from home with bikes on the trailer.

There isn't enough space on the forum to list all the goofs I've made... I think the first time I split cases it took me 4 tries to get it back together right. Worst part was cleaning off the Yamabond every time.

I can do it pretty fast now though! And learned a few time saving techniques... so wasn't a total waste of time.

While still learning about DTs, as I reassembled the clutch on my DT2, I didn't notice/know there are two different thicknesses of clutch plates! After continuing my education, another right-side teardown was necessary....

Need I say more.......
 

i am a screw up too
put engines together many time leaving a part out, such a bummer cleaning up the yamabond redo

How NOT to add a quart of oil to your engine: