tinu, You have come, as we say, to a fork in the road. The bike ran OK for you up until being subject to some really hard work, overheated and seized. So you could just put in your new pistons and things would be just fine. Maybe.....
Looking at what you have, for any serious fast riding or long distance reliability I would be inclined to strip it to the last nut and bolt. This engine has signs of heavy handed abuse in the past, such as bruising to the small end eyes, burred crankcase join where the breather passage runs. Previous posts mention important tell tale signs that all is not as good as it could be. All signs that whoever built it was not as good a builder as you would like...smacking pistons with a big hammer is not a recommended workshop practice. Stripping it will allow you to check every part and replace or refurbish as necessary.
The camshaft is also showing signs of wear, so easily replaced or gently stoned smooth, depending on your budget or future plans, while all is apart. Cam followers will also be wearing, so again, check here. The crankshaft sludge trap can also be checked, this is a well known failing.
The con rods need to be checked by your machinist. If they are bent, replacement is the only sensible option. Big end eyes need checking for ovality, and if they are found to be at fault, they can usually be reworked. Have the small end bushes replaced and accurately sized to match the new piston pins. A good firm hand push fitting at room temperature is about right. With the pistons warmed up with a heat gun, the pins will slide into place, needing just a little hand pressure. No need for violence or big hammers. Have the rods polished to remove nicks and burrs, and matched for weight.
Check the crank cases are a matched pair. With the engine removed you should find matching numbers stamped on the front faces of the cases, below the dynamo mounting, hidden by the front engine mounting plates. Mis-matched cases are not the end of the world, but could possibly be a factor in your problems.
Compared to modern machines, this engine is relatively simple to work on, but requires attention to detail, extensively covered by the thousands of posts on this forum.
At the end of the day it is your choice, depending on your budget and how much reliable use you want from the bike.
Swarfy.