What is the difference between a M74HC4520 and a 4520? Same chip with two different numbers or different chips?
Different chips. The 4520 is traditional 4000 series while the 74HC is a TTLish CMOS version, which is much more modern. Google CD4520 for the TI traditional cmos part. The big differences: CD4520 has a much higher supply voltage range, is much slower, and has much less drive current capabilities.
There's a bunch of counters in the 4000 series if you only want a single. Some have more bits or are presetable. Depends on what you're after.
The V and D would be manufacturer dependant (whoever they were), but to me it looks like a straight up traditional CMOS 4520.
(Perhaps a little history helps. When the 7400 "HC" CMOS series variants came out there was now an opportunity to merge the 4000 series in with them since the technology was essentially the same. They just tacked on the familiar 4000 part number onto the 74HC sequence. So the venerable 4046 PLL which people were familiar with was available now as a 74HC4046, with some very much improved specs. Before this wasn't possible because the previous versions of the 7400 series used bipolar transistors.)