Finally got round to pressure testing the RT1 and found the head gasket leaking, not sure if that's the only leak but will obviously re-check after it goes back on.
Head wasn't flat so a couple of hours of flatting and it's good to go.
Thought I'd take the opportunity to give it a de-coke and have a look at things.
Original bore looks okay ring gap slightly above top limit but nothing I'm concerned about.
Will give bore a light hone.
Some light scuffing on the piston, let me know if anyone thinks it's a problem.
I confirmed the markings the previous owner had put on the flywheel are spot on.
I gave the head a quick going over with my bead blast and I think it looks great.
Cylinder is waiting for the VHT paint to arrive tomorrow.
     
Nice to give the RT1 a little love, it's all been about the 175s lately
 

Few more pics of the head
     

Head looks beautiful!

piston cleaned up nicely and blasted head looks killer!
are you planning to put new rings into honed cylinder?

Msavitt, I'm not replacing the rings.
Although the end gap is slightly over top limit they look fine and the bike was running well.
Also, in another thread when I was sorting out the top end on my CT1-C I had checked the bore and it was fine.
I checked the rings and the gap measured near top limit so I measured a brand new set and they were also near top limit.
MarkT chimed in and said something along the lines of don't be surprised if new rings measure towards the top limit, so since then I've taken a more relaxed approach to the ring gap tolerance.

Piston kit would be a good idea as probably some reasonable priced ones still out there. Did you check the piston clearance. Just slide it in the bore with a feeler blade until you find a good fitting one. Gives a good enough idea for now. Possibly have about .060mm clearance stock. I'll go look.
Ok book say .050mm clearance. Piston had a 'lot of blowby carbon buildup. Talking pressure testing. My mate did a customers RT1 & it came out everywhere from how the liner is cast in & came out around the top i believe too. Think he just rode off wishing he hadn't had it done. Particular bike had a history of eating pistons, seizing & melting piston but gotta let them be rich & don't try to make then run perfect or they'll bite when you roll the throttle back from speed. Anyway, yours has lasted the distance so no reason to suspect it won't continue.
That was .050 for an RT2 by the way 045 to 050

Thanks for the input Morley, piston and bore are spot on so no need to replace just yet.
As I said the bike runs great until it fully warms up and I get a bit of surging off throttle, which I understand is something the RT1 is known for.
I only popped off the top end because of the leak at the head gasket which showed up when I did the pressure test.
 

How about pressure testing again incase like i said, coming up the outside of the cast in liner. They are a good sealing head normally. Might be better not to know haha.

Will be retesting it later, since all I've proven so far is that it was leaking at the head gasket.
I tested the other areas with soapy water including the mag side crank seal and they were all good.
The wet side crank seal hasn't been checked yet, so if it fails the pressure test again and it's not the head, then I'll pull the clutch cover and check the crank seal.

After five unsuccessful attempts to get the head gasket to seal I'm of the opinion the cylinder liner is no longer sealing to the outer casting.
There's a two psi drop over four minutes and a soap test shows bubbles in the same place where the cylinder and head seal.
I re-checked the head and it's definitely flat and smooth.
Plan is to remove the cylinder bolts and get the cylinder skimmed to the same level as the recessed liner and make my own copper head gasket to cover the entire sealing face.
I like a project, I will update on the progress when there is some.