Hello all,
What do you think about this?

photos.app.goo.gl/TPhvCWQQQ6VL13Ry8

I need a replacement barrel?

(it is more the missing(?) material around the port than the seize witness marks that is concerning me)

Thanks,
Mike

intake port debris
try muriatic acid to get rid of alum smear on the iron bore

It looks more like piston material was added than anything removed...  I've seen worse clean up just fine.  Just make sure you solve the issue that caused the problem.

Thank you!
So the exposed cylinder head material above the port… that isn’t because a lump of bore sleeve has gone missing?
Thanks.
Mike

The cutout in the center of the photo above the intake port is the rear boost port.

If I have any concern, it would be that the cylinder is already bored to near the maximum...  why? 
Because the top of the boost port is normally at the same height as the height of the other transfer ports.  That port is cut into the sleeve at an angle so as the cylinder is bored larger, the top edge drops lower.  A good shop will correct this after boring. 

Ok… thank you.
When i got the bike is was running well but then broke a ring… after which it was re bored to +1mm. So should be some life in the bore.
Why it seized? Don’t know yet and am investigating as best i can.
Good news for me that the boost port shouldn’t be an issue.
Subject to a bit if fettling to make the boost port height match the transfer ports.
Thanks.
Mike
 

That looks overbored far greater than 1mm to me.

You asked the question and I will give you the answer.

Get PJME of this parish to fit a new liner.

1mm over will be 67mm. If you can't clean it off & get another new piston kit then bound to be aftermarket kits out there going a bit bigger bore. Can we have a clear pic of the piston please, & if pos a clear one of the bore. Usual cause of melted piston is heat from lack of oil. Is there something going on there!!. Heat from a plug way to high "hot" in the heat range would likely melt a hole in the top. Of course nothing is ever as clear cut as it is in theory. I had an atv 4 stroke cylinder bored recently that looked like that so far as alloy smear goes & they didn't need it cleaned off first, wasn't a problem. But if it's mine & I want to just fit another piston I just sand it off with coarse emery paper but it's a pain of a job. Find what chemical melts it off but be careful. Then just buy a new piston kit & away you go. I wouldn't worry about ports not matching as that's the least of your worries but be sure they have a chamfered edge top & bottom. Also, is it definitely out to +1mm or did they just go first over which is 10 thou or 0.25mm. If it's out to 1mm then the poor old girl has a lot of stories to tell from the past.

Generally a seizure on the intake side , tends to suggest insufficient lubrication .
It might be wise to check over your oil pump at the same time .

the corner of that boost port has build-up of carbon or? that took out the bore and piston
standing by my first thought-debris