Thanks for the info. As I’m only splitting the engine to re-seal the case halves back together, I don’t think I will have to manhandle the LH case?
Thinking the job through, my main concern when removing the RH case is dislodging something that I shouldn’t / parts falling out.
I suppose for what I am doing, it doesn’t matter what gear it is in / neutral before I split it?
Thanks.

It's a myth that it has to be in neutral to dismantle it. Same goes for assembly. Providing the selector pins are in their tracks & the forks in their gears then you can be in any gear you like, or in between gears, so don't panic about that. When you think about it when the case is back on you can turn the drum & go through all the gears from 1st to top & if for instance its sitting in fourth gear when you fit the right case then you can only move it one gear to 5th in one direction the come back through all of them to 1st the other way. But you'll have to move one shaft a little to feel the dogs into gear although likely not every gear & just depends how they fall & might line up as you turn through to the next gear. You'll be doing this without the plunger & spring involved as just makes it hard work. But if you want to Click it through & feel each gear driving through to the sprocket then ok add the plunger & spring at that stage.

Nothing should dislodge or fly out. At least it didn't on this CT1-175 engine. In fact everything stayed put very well. I only used the duct tape as insurance because i was doing other work to the left case while i had it apart. 

If your just sealing the center cases it should go relatively easy and quick. As RT325 said in the earlier post neutral is not a must but i like to have the engine in neutral for disassembly and assembly. I also have the plunger and spring out for ease of shifting thru the gears before final assembly.

Forgot i took some pictures. here all the guts in the left case. 

You can see there 's not much to fall out of place. 

 

 

Yep just gotta be aware that if shafts lift up & go back into place, that selectors are still in place in the drum tracks & gear slots.

Yes, the AT/CT series have the shift drum retained into left case with an external clip which makes it easier not to have an issue.  DT400 doesn't have that but if you're careful, you'll be okay.

On the AT/CT if you're doing a "quick and dirty" case split leaving trans in the left case makes sense...  but if you remove the trans completely, I find it's far easier to install everything into the right case on that model...