Well, unless you are buying a 91 4 door, you don't have the option of getting an 8V in a 4 door. That is, unless you swap one in.
Timing belts rarely break. And if they do, trackick 16Vs are non-interference engines, so no valve damage will occur. At least that has been the experience of the people on here, that have tested to see if the trackick 16Vs are interference engines. If you are worried about it, change out the timing belt, at the recommended intervals, then you won't have to worry about it.
OBD1 and OBD2 are different types of systems found in vehicles, depending on what year they are. I don't recall the year OBD1 was initiated, but it ran through 1995. 1996 and up vehicles have OBD2. The main differences between them on trackicks are OBD2 trackicks have an extra O2 sensor, they have the coil built into the distributor and they have a crank sensor at the front of the engine. With an OBD2 system, you have to use a code reader to get the error codes from the ECM, where as on the OBD1s you just put a jumper in one of the plugs and the check engine light will flash the codes to you. Personally, I prefer the OBD1 trackicks....just a little simplier/easier to work on and not quite as much stuff to go wrong.
Here is some more info, in greater detail, if you really want to know....
http://www.auto-facts.org/OBD-2.html