I've noticed that most Advance Mark III magnetic RS ballasts are rated for two F30T12 lamps in addition to F40 and F34. Does this also mean I could use something like this to run two F40s?

http://www.1000bulbs.com/product/7845/BS-3022LP120.html

It's 0.67 amp HPF with F30s, while the Advance Mark III is only 0.61 amp with F30s. The OCV is 240. It's also the same length as a HPF F40 ballast and is reasonably priced. If this will run F40s, then it's essentially a drop-in replacement for the old banned ballasts, except that it's not banned. My only concern is that the OCV may not be quite high enough. What do you think?

I would guess it will underpower the lamps.
The high primary line current does not mean high secondary current, it depend on what power factor and losses the whole thing exhibit. You have to really look on the secondary current and nothing else.
The habit of using the primary current figure to distinguish between "full power" and "shoplite" came, when the ballasts were designed for F40 only and those came in just a few distinct breeds, where the the low primary current was somehow correlated with the real lamp power. But this correlation was just a coincidence for those few types. Don't forget, the F40 behaved all the same way and need the same treating among all makers. So when someone wnted to make full power ballast, he have to feed 0.43A into a 105V arc and provide at least 240V for start, he end up with a ballast with just 240V OCV, so the secondary current transformed to the primary become 240/120*0.43=0.87A for single lamp full power NPF or 240/120*0.27=0.54A for "shoplight" NPF. When a HPF was desired, a means to compensate the phase was included so, the power factor went up to the maximum. As the load behavior was fixed (F40 lamp only), it was possible to make the PF where you want it (it usually ends up at about 80..90%, as a result of an optimization for ballast losses vs size and cost), what mean with some ballast losses an input current of about 0.45A per lamp.
But when you want to extend the range too other lamp types, you can never reach the maximum power factor for all of them. Then the whole thing is usually optimized for to minimize the power dissipation with the worst case lamp.

Given it's claimed compatibility with F30, I think the ballast will deliver only current rated for F30, so about 0.36A.
As the F40 have different arc voltage, the power factor would be lower, so even when the real power is way below 40W per lamp (I would guess about 30W), the input current would be still quite high. And that mean it become equivalent to the "shoplight" ballast.