That "kit" is already balanced according to the ad. Eagle DOES sell pre-done "drop in" kits. I would guess it's one of them. Call Eagle and ASK.
I would not recommend that kit. It has a cast steel crankshaft. Those are the ones we've seen problems with. They're not as rigid as a factory nodular crank, and not as elastic as a forging. In our industry, when the word "steel" is used to describe a crankshaft, "forged" is implied. Engine builders, except those trying to mislead for a sale, won't call a cast steel crankshaft a "steel" crank. They'll include the word "cast".
If you DO buy it, as SS says, you'll need a new balancer and flywheel/flexplate for "internally balanced". The stock 400 stuff WILL NOT work.