Its a tight fit for the second PSU, but I think there is a 1/4" air gap when the case is closed, so plenty of room for the PSU to take in air.
That's NOT enough space for proper cooling on the second PS.
It WILL have overheating issues if you are running it at a significant percentage of it's full capacity - ballpark estimate if you're running it at more than 25% or so of capacity, it WILL start overheating due to LACK OF AIRFLOW.
I would strongly recommend figuring out how to flip it over to draw air in from the "down" direction, or figuring out how to get it AT LEAST 1 FULL INCH of clear space between the fan intake and the case.
The CPU shouldn't be a issue either way, G-series dual-core Pentiums don't soak a lot of power and a mining rig doesn't tend to push them anyway.
It's amazing how much CPU cooling has upgraded since the "meltdown" Pentium 66 (the last of the 5v CPUs) - which only soaked about 18 watts at MAX yet had overheating issues bad enough Intel never released a 75 Mhz version....