1979 or 390 rebore/how many times

removed engine from bike today,brought this bike as non runner put some fuel in her and she ran,so i took off head piston is like new ? no carbon in eaxhaust ports strange,top of piston says .060 (1.52mm)wich i think means 3rd over bore correct me if wrong please,as i no nothing of bike, bore is good little corossion on top 15mm was looking to rebore and replace piston anyway,can i go 4th over bore and can you get piston this size,and what size piston would i need ? would it be a 85mm piston is there such a thing
measured bore with vernier and it measures 83.34mm and the piston measures 82.70mm but that doesnt make sense as led to believe standard bore is 83.00mm

Here's a piston reference chart at Huskyclubs homepage.

I'd guess it's a 1st over bore size you got.
According to the list is std bore 82,92mm and 1st bore is 83,42mm.

Quoted from the list:
Sizes shown with comma are the catalog listing size and tend to be the bore size required for piston.

Because the piston is stamped with .060" on the top , could mean that it is a Wiseco oversize piston to suit a '76 CR360, which has a standard bore of 82mm. I am pretty sure that the oversize 360 pistons will fit the 390.

yes

so it could be a 3rd overbore piston for 360 wich is 83.42 correct mine is 84.34 ? so im only looking at second overbore wich is good for bike 30 years old,any explenation why piston is so clean and ports ?so i will be looking for piston 83.92 does this seem about right guys cheers for help