Feudalism supports 5 for town, 2 for city, and 1 for metro. Corruption is same as Monarchy. Mil. police is same as monarchy. War weariness is a factor, however, which is the same as republic. Use feudalism if you have a lot of military units, mostly towns, and aren't planning on staying at war for a long time. 3 support for extra units is crap, really.
I modded feudalism a while ago to have 6.2.1 support, communal corruption (due to the decentralized government) and 2 support for extra units. I haven't had a chance to try this out yet, but I think it's gonna be just fine. Other suggestions people have made is for the government to require "no maintenance", and then to compensate for that, not allow hurrying of production. I haven't done this though..