That sounds a little... Excessive? I wasn't even planning on balancing my rotating assembly as this is going to be a very mild build. The 306 windsor I built that regularly turns 6600 RPM didn't get balanced, 50k miles later it's still running strong.
My 428 was actually a rebuilt short block that was never run and then sat for a long time. I pulled it apart and had the crank polished and along with a quick hone of the cylinder walls and lifter bores.
From what I've gathered, I would simply use a regular spacer with a stock 390 balancer and matching flywheel?
You are correct that a regular spacer and a stock 390 harmonic balancer will work with your combination. However, a 428 crank will normally use an externally balanced flywheel. These flywheels have a 28 ounce weight of some sort attached to them. If you have the flywheel, see if it has that weight on it. If it doesn't, look for evidence of balancing on the crank, there would be some slugs of mallory metal added to one or more of the counterweights on the crank.
If you just bought a 428 engine with no flywheel, I'd bet that it wasn't internally balanced, and you will need a 428 flywheel to make it work. You could probably get away without balancing if you KNOW that the 428 crank was not internally balanced, and you have a 428 flywheel, or if you KNOW that the 428 crank was internally balanced and you have a 390 flywheel. If you aren't sure about this, I'd really suggest you get it balanced. If you put a stock 428 crank together with a stock 390 flywheel, you will have a significant vibration problem.
Jay, I was planning on using a 428 specific flywheel anyways:
https://www.summitracing.com/parts/fiz-186541/overview/make/fordI have a ACT lightweight flywheel in my '69 and absolutely love it, the Fidanza unit actually has provisions for an external balance and internal balance. I'm assuming this is through a weight that is simply bolted on (I had a McLeod flywheel similar to this).
The flywheel is unfortunately missing, however, there isn't any evidence of the crank being balanced; there aren't any slugs of mallory anywhere.
