Looks like that shock may be able to be pulled apart if you want to keep the shocks to use as a full restoration that isn't used in competition, new shafts aren't the hardest thing to turn up from hydraulic ram shaft of the correct size
New shocks are really your best option if you plan on using it

I bought a seat from Sammy Miller products for my C a few years ago as it was missing. Base is fibreglass from memory & you have to use your original mounting brackets, front bracket is really common but the rear are unique to the C onwards. TY trials & Yamaha majesty both have kits available now ...

From what I've read on ozvmx photobucket have gone nuts, wanting something like $300 a year to allow posting on sites. They've really gone backwards this year & are going to lose a lot of business

Closer to home Julz there is a guy in Auckland who may be able to help, can't remember his details but when I talked to him about a Sherco stator he said he'd done a lot of other trials stuff
From memory we didn't proceed due to him saying whichever coil was the problem had the thinnest wire he'd ...

600C is definitely higher than the only sleeve I've had in & out before required.
My CZ only requires about 200C to get out, throw it in the oven cold sitting on the sleeve & turn on to 200, come back an hour later & the cylinder has slid down the sleeve
Can't suggest anything else

Only suggestion I can make is to build the port up using tape inside the casting before fitting the sleeve then blend things afterward

When I removed all external signs of my Ty's oil pump on the sidecover I just used the tape on the inside of the cover & folded up around the gasket surface to form the barrier, the JB weld made contact with the glue side where it was exposed. Came off fairly easily
http://i788.photobucket ...

Not too hard to stop it sticking to liner, the advantage of using it is how it's liquid so you can use tape etc to form dams where you need it to be.
Biggest real problem is that you'd have to do it with the cylinder lying on it's side & only do 1 side of the port at a time
I've been a bit sceptical ...

Not unique by any means, the same part is used in early RM100 & 125s & a lot of TS models, pretty sure the 1 I got was out of a TF farmbike
This is the new part number & a small example of what uses it, the original part number was 64110-38000
m

Hopefully that helps you to find a hub from a wrecker ...

Your main bearings are worn if you are getting movement at the flywheel, mine was still on standard bore a few years ago & started running erratic on the second day of a 3 day trial so I decided to have a look what was going on
I was able to remove the flywheel without a puller - first clue ...