since the crank is localized I would think you could run your finger across it and possibly feel sand or feel a crunchy lower rod bearing. I'm guessing no sand got in. thinking combustion cycle would proportionally suck from least resistance at reed valves first??

"champion spark plug" free adaptor for dial gauge.
Just knock the ceramic out, then drill and tap hole in side. of course, you may want a more professional setup.

The "gasket sand" might be corrosion. 

But even if it isn't, you'd see the effects of ingested sand on the piston skirt.

Yes you can't see it in the pix, because I cleared it off, but in the triangle pockets there was a stash of very fine sand ( I guess it could have been some sort of corrosion ), so it managed to get in, that was why I was worried that it may have wormed its way out too. That all said the piston fits in the cylinder sweet as a baby's bottom so I think I may just grind out a few more kms on these rings and next time round do the new rings and hone business.
PABT I am all for efficient solutions, given the price of digital dial guages that is something for the future too. I just hate scraping the gaskets (doesn't everyone?) but I am tidying things up a bit.

My wife says I never clean the bowl, but I made an effort this time!

There's a little pitting on the cylinder base ( it doesnt appear to be too serious )

a little tidy of the transfers

(reading on the forum, I'm under the impression there could be some issue with posting pictures / links clogging up the site, please let me know as I post a lot of pictures, but I am happy to stop and just add a bit of text now and then)
anyway here is the intake

The hosting of pictures directly by the site is broken right now. 

No problem at all with using a third party host for your pics like you've been doing. 

Great, good to have that confirmation

and the exhaust