Stock flex plate reuse is fine if the converter is the same balance as the one you took/take out. Same for the weights.
You can get the converter allready balanced for a 360 or use the B&M flex plate for neutral balanced converters.
Pistons at .030 and the same compresion height will add a little (And very little) more to the ratio. If te piston height has changed, gone up in height, then ratio's can change dramaticly. This is the key and why theres a need to measure the pistons depth. (And valve reliefs if any)
