I've got a '91 import with the 2.8. I can't tell you much about the 3.1, but it's a very similar engine. A lot of people out there are fans of both. The 3.1's indirect injection and they added more electronic controls and emmissions stuff I think. If you haven't already checked it out this site's a good resources: http://www.itocuk.co.uk/forums/
Parts seem to be easy to get from Australia or the UK and of course NA trooper parts swap over in some cases.