do you have any pictures on your port job...?
Did you take the base gasket away or replaced it with a thinder one... ?
no, I don't have any pics.
Basically you are the right track except for one thing - do not change the bridge dividing the upper and lower transfers. Where you put that red line, do not do anything there. For the lower transfers, work on the bottom lip. Chamfer it and create a slope down to towards the bottom. Upper transfers widen a wee bit towards intake. Exhaust and intake can be widened a bit but I would have to look at everything to see what the limiting factors are on that cylinder and piston as I don't remember off the top of my head
Yes, you can just remove the base gasket or make a thinner base gasket as required to achieve approximately .020" clearance. On most Husqvarnas I have found totally removing the gasket gives a little over .020" but you have to measure each saw to know for sure. Use an appropriate sealer like Permatex Motoseal, Dirko, Hondabond, Yamabond, etc.
I never do anything to the pistons. I personally think its a waste of time, but I also have never tried it. I like my saws to be improved but I don't chase after every little bit of performance.
The 262/261 cylinder is very similar in design to Stihl 044/440 046/460 cylinders. Do a lot of reading and looking at porting pictures before you start grinding. Make sure you understand the limiting factors of widening ports (ie, ring end locations) and make sure you understand how to bevel the port edges, and how much to bevel them as well as understand correct port shapes. Read, read, read some more and look at lots of porting pics before you grind.
Lastly, I would suggest grinding on a cheap aftermarket cylinder first, or on a used jug that might have some damage already like light scoring.