What is not fitting? I run a 4.88 geared V6 3rd in my '85 housing. Usually you may need to grind a bit off the two notches in the housing to let the ring gear teeth fit past, I had to do that with the 5.29/4cyl 3rd I used to run. I also find that opening up the mounting holes in the 3rd a tad helps a great deal. I use a bit that is 1/64" to 1/32" larger than the existing holes to make it easier to slip the 3rd member in place over the studs. Makes it so much easier when you are laying on your back trying to wrestle the thing into place.