Cast pistons are lighter than forged - much harder to balance once the cast pistons are swapped. You would have to weld up the crank.
A piston swap IS basically rebuilding the engine, you have to completely dissasemble the engine, so why wouldn't you put in new rings and bearings while you are there?
Cast pistons are actually better than forged in many cases: they are lighter (engine rev's quicker), typically have a good flame front, and are designed to last. They are not better in cases where you are abusing the piston itself, IE detonation, ton of boost, etc.
A cast piston will handle some boost and nitrous oxide (I have a cast piston 440 that has a 200 shot on it, never a problem and that engine has seen a LOT of NOS), just don't get crazy with it. A cast piston isn't going to want a 400 shot and/or 15 lbs of boost, it just won't be strong enough.
That is where a Forged piston is better - more strength, so things like a lean condition, excessive boost, ect don't affect it.
If you are building under 1.5Hp per CI, including all of the power adders, cast is the way to go in my mind.
I always like to have a spare engine and parts (hence the reason I want to get rid of the olds, it was an orphan), so my suggestion is to run what you have, enjoy, and build another one on the side. Right now your season is ended 'cause you don't want to run what you have. Run it until you can't.
