Jahns pistons

Well that is a dome piston. Still need to see the underside where the connecting rod goes in to figure out if it is forged but if you are not going huge power I would not be worried. If you look up in where the wrist pin is and it has cross hatching then it is definitely cast. This is usually the only place to tell if it is cast vs. forged. A forged will never have the cross hatching there internally but even a cast piston could have them removed. However, there would very few people (if any) that would want to perform custom machining on a cast piston because it is still just a cast piston. If anything you will need to watch your valve clearances if using that piston since it will go up into the combustion chamber as it is. Do you have the heads that were used with the previous build? I would ensure that you look them over closely and ensure whatever heads you decide to use have the same clearances.

Edited for literacy issues. I cannot think, I has the beer.