I have a 1992 b2200. On really cold mornings there is a loud clacking noise on start up.it only lasts a few seconds and then it runs fine. Could this be a faulty oil pump?

This is probably hydraulic lifter noise. There are a number of possibilities, but more common ones are using an oil filter that doesn't have an anti-drainback valve and oil of the wrong viscosity for the temperature range.

My 1988 B2200 has made this same sound ever since I got it in 1994, and it has only 121K miles. The former owner even told me this before I bought it. It's lifter noise, not oil pump, just make sure that the oil level is OK, and the anti-drainback oil filter might be a good idea. I use standard Fram orange oil filter, and change oil every 4K miles. I wouldn't worry about it, these trucks all have this "issue".