There should be a ton of pick and pull type junkyards in MN and I bet if you start searching in those you will find a motor and trans that might just need a slight freshening up to get you by until you decide to rebuild it the right way. From what I've seen, MN is one of those places with a bunch of old cars.

Here is a huge list of some junkyards in your State. Some specialize in cars that won't be of interest to you, but I bet if you get on the phone and let your fingers do the walking you can find one of these with some Pontiacs sitting around.

http://www.usedpartscentral.com/search_minnesota.htm

Don