The 4-F32T8 ballast will work fine with your F40T12 bulb. It's just not as strong as a 4-F40T12 ballast - but I haven't been able to find an electronic ballast designed for four 40watt tubes, only magnetic. Electronic ballasts are mostly used in industrial applications, because they're efficient and quiet, with low power consumption, and F32T8 bulbs are mostly used in industrial apps because they are also more efficient as well as smaller (less packaging, waste, etc.).
The short answer is - the 4-F32T8 ballast will still make that 40watt bulb glow like crazy
