Change the cam to something close to the OEM size HP cam and be done with it. You will be spending quite a bit to change pistons. Really not worth it for a street car.

So it won't be optimal. Big deal. Cast crank is fine. Just get a balancer and torque convertor setup that will match. B&M used to make a flexplate that takes care of the weight on that end. That leaves you needing a balancer.

I would also go ahead and paint it before storing.