Thanks Mr. E! I have compiled your fork and it worked without errors. If I remember right the error you mention (ambiguous type conversion) was also the one that prevented me from compiling a123's last code.
I had a Slimcoin crash recently but that was because I was running it with very low memory & swap after a reboot.
I also would like to keep the 3-way generation if possible, but I need to make sure I understand what the issue with PoS was first. If I've got it right, the problem was that stake transactions would end up creating a whole bunch of small credits, and then each one of those would be a candidate for future staking which led to too much processing (searching a huge stack of transactions constantly). If that's the case, then I'll need to understand better how staking actually works to know whether it's fixable or not.
I'm not at all familiar with Peercoin, but I can't help thinking -- did they have this problem? Did they solve it?

Unfortunately I don't know if Peercoin had this issue or if they resolved it. I never had problems or crashes with my Peercoin client.