Our Mini had a 2:45 fastest lap against that sprite at Buttonwillow, but our average "fast laps" were 3:15ish.
If you are thinking of driving a slow car, here's my advice based our 1 experience-- get the BIGGEST rear view mirror you can fit into your car and USE IT and point EVERYONE by leaving plenty of room on the race line. At least on the first day. That doesn't mean you won't get hit (the race-winning Volvo dive bombed us clipping the front because they didn't want to go the direction our driver pointed, apparently).
Here's our "race line" when someone came up behind us.
http://www.youtube.com/watch?v=47bXIdb9oxc
That was our behavior on day 1. On day 2, we tried a little harder to put our foot in it-- particularly Jerry who can be seen actually PASSING a car in this video (starting at about 4:30 into the clip until the end).
http://www.youtube.com/watch?v=mSOgw5uED4A