As far as internal or external balance, if your block uses a 2 piece rear main seal then it is an internal/neutral balanced crank, meaning that you don't need an external counterweight on the torsional dampner/harmonic balancer or on the flywheel to balance the rotating assy.
If the block is a one piece rear main seal type it will need a flywheel made for one piece seal engines as they have a counterweight built in that replaces the weight removed from the crank to make it a one piece seal type making it an external balanced assy.
Most all small blocks were internally balanced until the advent of the one piece rear main seal design with the exception of the 400 that used a counter-weighted balancer and flywheel because there wasn't enough room to add the weight to the longer stroke crankshaft economically for internal balancing. Sorry for being so long-winded.
If your rods and pistons are stock the Scat crank should be close enough for mild rpms as far as balancing goes. You need to call Scat and ask one of their salesmen for yourself. If it were mine I'd probably get it checked, but then again I'm picky and go overboard too often.
As far as noting that it was steel vs. cast iron I didn't even know that there was a jury out on the subject. I ***umed that for one if they were making it out of a more expensive base material that it was because it was to make a higher quality product. At least I thought steel was more expensive than iron. I know that it has more torsional and tensional strength before failure. How many bolts do you see made out of iron? All of my wrenches, screwdrivers, hammers, jacks, toolboxes are made of steel. I can see that perhaps iron is harder and may wear longer if dirt were to get into the oil, but isn't that what the oil filter and the bearings are supposed to take care of? I've carried my 112 Buck knife for 30 years and have yet to see one with a cast iron blade. Forgive me if I ***umed steel was a better material for a crank.