balance problem need flywheel advice

I've pretty much completed my 360 build, gettin ready to drop it in my slant six demon, and adding 4speed. Much thanks to some of the guys that have helped me along the way. Next roadblock:

I've got a 360 harmonic balancer on the front but I think I have a 318 flywheel. I'm gonna post a picture. My problem is my machine shop resurfaced it for me but told me it doesn't need balancing. I dont see any evidence of balancing on it.

I called 6 different machine shops and only 1 said could balance my flywheel, but only to within 80 to 90 percent (and for $150). I guess I should have had the engine balanced before I assembled. Is it possible to get locations of where to drill (partial) holes and how deep to get it "close" to balanced. In other words do it myself. I've heard 360 engines were never balanced that good straight from the factory anyways. Or am I crazy?