When I did the 351w swap I had to do something with the flywheel too. I don't remember which I had to switch to/from (28 to 50 OR 50 to 28), but a local balance shop was able to rebalance my flywheel. It was pretty cheap to do and since I had only run a few thousand miles on that flywheel it was the best choice I found. Didn't even need to re-surface.