273 torque converter

Yes, the converter is neutral balanced.

Yes, you need an offset balanced flex plate or the weight set and weld them on.

Yes, you will need an annular ring because of the front snout size difference. Check the inside diameter of the magnum crankshaft and report to member “CharlieS”, he makes and sells the annular rings to make up this difference. Most go into standard LA motors, that’s why you need to actually measure your magnums register size.