EBC are ok but they are not peak performance which you seem to be after.
An example of someone who does it below but you coould find someone who does it for forklifts or the like locally to you.
https://villiersservices.co.uk/product/brake-shoe-re-lining-service/
It takes some time for pads to bed in and have full contact with the drum.
You might want to go down the path of having pads of a suitable friction material applied to the brake shoe so you can match the diameter of your drum.
What happens if you give the throttle a big blip when it starts revving up?
Could also be starved of fuel if there is not an air leak as Lemur has suggested.
When you pull the clutch lever in I assume you can feel the mechanism trying to activate the clutch?
Also I assume you have tried riding it in a high gear with the clutch pulled in while accelerating?
On my gasgas enduro bike I went to the shop and bought a cheap ring spanner and ground the outside down until it fit.
Scientific torque spec I used was almost as tight as I could do it by hand and then give the the spanner a couple of light hits with a hammer.
Trials bikes are normally fairly difficult to change into neutral, I normally just turn my bike off then put it into neutral.
On the odd occasion you can knock it into neutral with it running but its certainly not really easy.
https://www.trialsbike.com.au/product/ossa-5020040211-air-filter-box-lid/
Was an Ossa dealer at the time, so he may still have a stand if you send him an email.
Another thought, you could see if a sleeve was available for the seal area.
Then just give the bearing area a light cleanup with emery. https://www.skf.com/au/products/industrial-seals/power-transmission-seals/wear-sleeves/skf-speedi-sleeve
You could investigate getting the damaged areas chrome plated.
They would grind the part down and then chrome plate back to size, hopefully removing the damage in the process.
The seal area is the key, I don't think it would matter if there were a few surface defects like what you've got where the bearing sits.
If the depth of the defects are less than 0.25mm than it should be acceptable to chrome plate.
Have you checked the HT coil, spark plug and lead?
Not sure but it wouldn't surprise me if the electronic ignition kit for an SWM would fit.
https://www.motoswm.co.uk/shop/swm-rotax-trials-electronic-ignition-kit-pro/
The spring/open side faces inward so that when pressure is applied from the compression of the fuel mix in the bottom end it energises the seal.
If it is the other way around only the spring/material strength is what is creating the seal which should be enough to keep out the air or gearbox oil which is not under a relatively high pressure.
Plus one to Jonnyc21, has been crushed in shipping, the split is normal though.
You might be able to buy the bush from a local engineering/bearing supplies store or online rather than getting Honda parts if it is not a special size.
It is a glacier bush, very common part.
Kill switch should be easy, You need to connect it between ground and the wire that goes into the HT coil.
The regulator is normally not part of the flywheel/stator, generally it is located up in the area of the frame above the engine.
Be 6ft tall and kick it like you mean it.
I stood slightly forward of where you normally would so you could get a good kick at it once the starter gear had engaged.
If you can get your hands on a head for a 2011, this has a lower compression than the 2013 had.
Not sure if the 2012's had the higher compression or not but I had both a 2011 and 2013 model.
Depends how/what you ride but I found the 2013 to be a big improvement in power with the higher compression giving a much more torquey engine.
