the bolt patterns between the 3 speed and the 4 speed is different.
There is a good chance that the 4 speed will bolt-up to your current bellhousing because many of the later aluminum bellhousing had both the both patterns on them. (look for the holes with yellow paint in the photo below)
You will need to go under the car and look to see if your current bellhousing is one of these multi-bolt pattern types.
Here is a lot of additional info on this swap so read thru this article and ask questions.
DD
http://www.slantsix.org/articles/4-spee ... speed1.htm
