Yes you can. All Geo Metro engines are compatible from 1989 - 1997. Just make sure that they both have the same transmission or you'll have to do a lengthy and expensive conversion.
Interesting question, and I give you credit for your creativity, but no. Consider the overall sizes of the pickup's engine compartment vs. the geo's. A Cummins would be more likely as you'd be going...
Code 46 is the trouble code for the Idle Speed Controller which is that big black box thingy on your throttle body. A lot of Chilton-type manual books omit that code because the ISC isn't found on...