My Cessna 150 uses an O-200A, they like to gum up valve guides every 300 hrs or so. You'll see people online pushing the use of "the rope trick", it fixes nothing and is only a band-aid solution. The proper fix is to ream the valve guides, it can be done by a skilled mechanic without removing the cylinders. Most O-200 guys swear by a little glug of marvel mystery oil in the fuel to help alleviate the problem.
The O-200 loves mogas, I typically mix Avgas to Mogas at a rough 40/60 ratio.
The bottom ends are known to be strong but the old continental cylinders can get a little soft. Although 68/80 psi would not scare me away from an O-200, anything lower is getting concerning. New Millennium cylinders will tighten an old O-200 top end nicely.
The oil pump gears can get a little out of tolerance and the pump loose its prime if not flown regularly. It's annoying but can be re-primed by removing the filter (if equipped) and squirting some oil into the orifice. If not equipped with an oil filter the oil change interval is cut in half to 25 hrs and screen must be cleaned every oil change.
I've never experienced carb icing in my Cessna but I know people that have and generally it is agreed the O-200 makes ice like a Frigidaire. Proper use of carb heat is important.
Parts are readily available, but nothing is cheap these days.
TBO is 1800 hrs, as a previous poster mentioned the old continental cylinders will likely need at the very least rings around 900 hrs.
The O-200A citabria has an exhaust system that maybe hard to find parts for, I've seen them modified to accept champ / Cessna 150 style exhaust systems. I am not sure if this would be a legal repair.
I've only done one circuit in an O-200 equipped 7eca Citabria and I liked it, I kind of regret not buying it. It didn't have power to spare but it was adequate at near sea level with two adult males and 15 degree C day to climb at 500 ish fpm.
Hope this helps
